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Superconducting energy gap of YB 6 studied by point-contact spectroscopy
Microsoft Academic Search
Yttrium hexaboride has the second highest critical temperature, Tc?8K, among all borides. The presented paper deals with the experimental study of its superconducting energy gap established by the method of the point-contact spectroscopy. The temperature dependence of the energy gap and the strength of the superconducting coupling is presented.
Pavol Szab¾; Jozef KacmarcĒk; Peter Samuely; Jßn Girovsk²; Slavomir Gabßni; Karol Flachbart; Takao Mori
Complex gap in color superconductivity
SciTech Connect
We solve the gap equation for color-superconducting quark matter in the 2SC phase, including both the energy and the momentum dependence of the gap, {phi}={phi}(k{sub 0},k). For that purpose a complex Ansatz for {phi} is made. The calculations are performed within an effective theory for cold and dense quark matter. The solution of the complex gap equation is valid to subleading order in the strong-coupling constant g and in the limit of zero temperature. We find that, for momenta sufficiently close to the Fermi surface and for small energies, the dominant contribution to the imaginary part of {phi} arises from Landau-damped magnetic gluons. Further away from the Fermi surface and for larger energies the other gluon sectors have to be included into Im{phi}. We confirm that Im{phi} contributes a correction of order g to the prefactor of {phi} for on-shell quasiquarks sufficiently close to the Fermi surface, whereas further away from the Fermi surface Im{phi} and Re{phi} are of the same order. Finally, we discuss the relevance of Im{phi} for the damping of quasiquark excitations.
Reuter, Philipp T. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, D-60054 Frankfurt (Germany); Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States); TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada)
Noise and Bandwidth Measurements of Diffusion-Cooled Nb Hot-Electron Bolometer Mixers at Frequencies Above the Superconductive Energy Gap.
National Technical Information Service (NTIS)
Diffusion-cooled Nb hot-electron bolometer (HEB) mixers have the potential to simultaneously achieve high intermediate frequency (IF) bandwidths and low mixer noise temperatures for operation at THz frequencies (above the superconductive gap energy). We h...
R. A. Wyss B. S. Karasik W. R. McGrath B. Bumble H. LeDuc
Specific heat measurements of a superconducting NbS2 single crystal in an external magnetic field: Energy gap structure
NASA Astrophysics Data System (ADS)
The heat capacity of a 2H-NbS2 single crystal has been measured by a highly sensitive ac technique down to 0.6 K and in magnetic fields up to 14 T. At very low temperatures, data show excitations over an energy gap (2?S/kBTc?2.1) much smaller than the BCS value. The overall temperature dependence of the electronic specific heat Ce can be explained either by the existence of a strongly anisotropic single-energy gap or within a two-gap scenario with the large gap about twice bigger than the small one. The field dependence of the Sommerfeld coefficient ? shows a strong curvature for both principal-field orientations, parallel (H?c) and perpendicular (H?c) to the c axis of the crystal, resulting in a magnetic field dependence of the superconducting anisotropy. These features are discussed in comparison to the case of MgB2 and to the data obtained by scanning-tunneling spectroscopy. We conclude that the two-gap scenario better describes the gap structure of NbS2 than the anisotropic s -wave model.
Ka?mar?Ēk, J.; Pribulovß, Z.; Marcenat, C.; Klein, T.; RodiĶre, P.; Cario, L.; Samuely, P.
Anisotropic Energy Gaps of Iron-Based Superconductivity from Intraband Quasiparticle Interference in LiFeAs
If strong electron-electron interactions between neighboring Fe atoms mediate the Cooper pairing in iron-pnictide superconductors, then specific and distinct anisotropic superconducting energy gaps {Delta}{sub i}(k) should appear on the different electronic bands i. Here, we introduce intraband Bogoliubov quasiparticle scattering interference (QPI) techniques for determination of {Delta}{sub i}(k) in such materials, focusing on lithium iron arsenide (LiFeAs). We identify the three hole-like bands assigned previously as {gamma}, {alpha}{sub 2}, and {alpha}{sub 1}, and we determine the anisotropy, magnitude, and relative orientations of their {Delta}{sub i}(k). These measurements will advance quantitative theoretical analysis of the mechanism of Cooper pairing in iron-based superconductivity.
Davis J. C.; Allan, M.P.; Rost, A.W.; Mackenzie, A.P.; Xie, Y.; Kihou, K.; Lee, C.H.; Iyo, A.; Eisaki, H.; Chuang, T.-M.
Scanning Tunneling Spectroscopy of Superconducting LiFeAs Single Crystals: Evidence for Two Nodeless Energy Gaps and Coupling to a Bosonic Mode
The superconducting compound LiFeAs is studied by scanning tunneling microscopy and spectroscopy. A gap map of the unreconstructed surface indicates a high degree of homogeneity in this system. Spectra at 2 K show two nodeless superconducting gaps with ?1=5.3▒0.1meV and ?2=2.5▒0.2meV. The gaps close as the temperature is increased to the bulk Tc, indicating that the surface accurately represents the bulk. A dip-hump structure is observed below Tc with an energy scale consistent with a magnetic resonance recently reported by inelastic neutron scattering.
Chi, Shun; Grothe, S.; Liang, Ruixing; Dosanjh, P.; Hardy, W. N.; Burke, S. A.; Bonn, D. A.; Pennec, Y.
Scanning tunneling spectroscopy of superconducting LiFeAs single crystals: evidence for two nodeless energy gaps and coupling to a bosonic mode.
The superconducting compound LiFeAs is studied by scanning tunneling microscopy and spectroscopy. A gap map of the unreconstructed surface indicates a high degree of homogeneity in this system. Spectra at 2 K show two nodeless superconducting gaps with ?(1)=5.3▒0.1 meV and ?(2)=2.5▒0.2 meV. The gaps close as the temperature is increased to the bulk T(c), indicating that the surface accurately represents the bulk. A dip-hump structure is observed below T(c) with an energy scale consistent with a magnetic resonance recently reported by inelastic neutron scattering. PMID:23002767
Chi, Shun; Grothe, S; Liang, Ruixing; Dosanjh, P; Hardy, W N; Burke, S A; Bonn, D A; Pennec, Y
Energy gap and proximity effect in MgB2 superconducting wires
Measurements of the penetration depth ?(T,H) in the presence of a dc magnetic field were performed in MgB2 wires. In as-prepared wires ?(T,H<130 Oe) shows a strong diamagnetic downturn below ~10 K. A dc magnetic field of 130 Oe completely suppressed the downturn. The data are consistent with proximity coupling to a surface Mg layer left during synthesis. A theory for the proximity effect in the clean limit, together with an assumed distribution of the Mg layer thickness, qualitatively explains the field and temperature dependence of the data. Removal of the Mg by chemical etching results in an exponential temperature dependence for ?(T) with an energy gap of 2?(0)/Tc~1.54 [?(0)~2.61 meV], in close agreement with recent measurements on commercial powders and single crystals. This minimum gap is only 44% of the BCS weak coupling value, implying substantial anisotropy.
Prozorov, R.; Giannetta, R. W.; Bud'ko, S. L.; Canfield, P. C.
Doping and temperature dependence of the superconducting energy gap in the electron-doped cuprate Pr 2- xCe xCuO 4- ?
In hole-doped cuprate superconductors at low carrier concentrations two energy scales are identified: the superconducting energy gap and the pseudogap. The relation between these energy scales is still a puzzle. In these compounds a measurement of the energy gap is not necessarily a probe of the order parameter. In the electron-doped cuprates the pseudogap does not obscure the superconducting state. Consequently, the superconducting gap can be studied directly in a tunneling experiment. Here we show that by studying superconductor/insulator/superconductor planar tunnel junctions we are able to map the behavior of the gap amplitude for the entire (doping-temperature) phase diagram of the electron-doped cuprate superconductor Pr2-xCuO. The superconducting gap, ?, shows a BCS-like temperature dependence even for extremely low carrier concentrations. Moreover, ? follows the doping dependence of planes where d-wave superconductivity takes place [8]. In addition there are changes in the shape of the Fermi surface with doping [9-12]. On the other hand, there are several differences between these compounds, including the temperature dependence of the resistivity above (PCCO) with lead as a counter electrode. We measured the differential conductance at different temperatures and magnetic fields for the entire doping range where superconductivity exists. Fig. 1 presents the normalized (by the conductance at ?0H=10 T) differential conductance at various temperatures of the extremely underdoped x = 0.125. For each temperature we fit the data using a modified BTK model for a non-monotonic d-wave as described elsewhere [17]. From our fit we found that ? goes to zero at the critical temperature in a BCS way for the entire doping range, this is seen in Fig. 2. We made use of the absence of the pseudogap and the accessible upper critical field to measure the low temperature limit of the gap amplitude as a function of doping for the entire superconducting regime [18]. Our results are shown in Fig. 3. For the overdoped and optimally doped regions the gap follows the doping dependence of Tc as found for hole-doped cuprates. Surprisingly, this behavior persists for underdoped samples. For this doping regime, the gap amplitude decreases with decreasing doping, in strong contrast with the celebrated tunneling measurements on hole-doped cuprates [19]. In summary, we present the tunneling spectra of lead/insulator/PCCO junctions over the entire doping range where superconductivity is observed. We found that the gap amplitude follows the BCS-type temperature dependence. In addition, we show that for this cuprate the gap amplitude follows the critical temperature as a function of doping, even for underdoped samples. Our results are therefore consistent with a single superconducting energy scale, in contrast with the hole-doped cuprates. We note that for hole-doped cuprates probed by node sensitive spectroscopies and Andreev-Saint-James reflections one finds an energy scale which decreases with doping in the underdoped regime. This behavior resembles our findings reported here. Assuming that the hole-doped and the electron-doped cuprates share the same mechanism for superconductivity, we can conclude that for hole-doped cuprates the Andreev-Saint-James (and nodal) gap is the superconducting gap, while the pseudogap is a competing order to superconductivity.We are indebted to G. Deutscher, S. Hacohen-Gourgy for fruitful discussions, to M. Karpovski for evaporating lead electrodes. This research was partially supported by the Binational Science Foundation Grant Number 2006385, the Israel Science Foundation Grant Number 1421/08 and by the Wolfson Family Charitable Trust. RLG is partially supported by the NSF DMR0653535.
Diamant, I.; Greene, R. L.; Dagan, Y.
Normal state electronic structure and the superconducting energy gap in HTSC's as determined from photoemission spectroscopy
Photoemission spectroscopy has been utilized to determine the electronic structure of high-T{sub c} materials. The observation of dispersive bands at E{sub F} suggests a Fermi surface similar to that obtained from a band calculation. The results apparently are not inconsistent with the notion of a correlated Fermi liquid consisting of hybridized p-d bands. However, it is becoming more and more difficult to distinguish between Fermi liquid behavior in the new high-T{sub c} superconductors and behavior expected on the basis of the novel new non-Fermi liquid theories. The differences are now predicted to be on an energy scale smaller than our experimental resolution. We point out that, while deviations from simple band theory certainly do exist in the form of core and valence band satellites, band narrowing, and rapid photoemission peak broadening away from E{sub F}, there are sufficient agreements with the overall DOS that it should be considered a good starting point for the electronic structure. For example, the calculated Fermi surface for both the 123 and 2212 structures is reasonably well reproduced experimentally and the bands at E{sub F} consist of p-d hybridized orbitals just as predicted by local density functional theory. Our spectra clearly show that a BCS-like DOS is obtained at the Fermi energy as a gap opens up below T{sub c}. This is just one more indication that the old conventional models should be considered more seriously. 18 refs., 6 figs.
Arko, A.J.; List, R.S.; Bartlett, R.J.; Cheong, S.W.; Fisk, Z.; Thompson, J.D. (Los Alamos National Lab., NM (USA)); Olson, C.G.; Yang, A.B.; Liu, R.; Gu, C. (Ames Lab., IA (USA)); Veal, B.W.; Liu, J.Z.; Paulikas, A.P.; Vandervoort, K.; Claus, H.; Campuzano, J.C. (Argonne National Lab., IL (USA))
Model Evidence of a Superconducting State with a Full Energy Gap in Small Cuprate Islands
We investigate subdominant order parameters stabilizing at low temperatures in nanoscale high-Tc cuprate islands, motivated by the recent observation of a fully gapped state in nanosized YBa2Cu3O7-? [D. Gustafsson et al., Nature Nanotech. 8, 25 (2013)]. Using complementary quasiclassical and tight-binding Bogoliubov-de Gennes methods, we show on distinctly different properties dependent on the symmetry being dx2-y2+is or dx2-y2+idxy. We find that a surface-induced dx2-y2+is phase creates a global spectroscopic gap which increases with an applied magnetic field, consistent with experimental observation.
Black-Schaffer, Annica M.; Golubev, Dmitri S.; Bauch, Thilo; Lombardi, Floriana; Fogelstr÷m, Mikael
Bulk superconducting phase with a full energy gap in the doped topological insulator Cu(x)Bi?Se?.
The superconductivity recently found in the doped topological insulator Cu(x)Bi?Se? offers a great opportunity to search for a topological superconductor. We have successfully prepared a single-crystal sample with a large shielding fraction and measured the specific-heat anomaly associated with the superconductivity. The temperature dependence of the specific heat suggests a fully gapped, strong-coupling superconducting state, but the BCS theory is not in full agreement with the data, which hints at a possible unconventional pairing in Cu(x)Bi?Se?. Also, the evaluated effective mass of 2.6m(e) (m(e) is the free electron mass) points to a large mass enhancement in this material. PMID:21517345
Kriener, M; Segawa, Kouji; Ren, Zhi; Sasaki, Satoshi; Ando, Yoichi
Far-Infrared Energy Gap Measurements in Bulk Superconducting In, Sn, Hg, Ta, V, Pb, and Nb
Measurements of the onset of absorption due to excitation of electrons across the energy gap were made on a variety of superconductors. Using the onset of the main absorption edge as a measure of the energy gap, the values of Eg(0), the energy gap at absolute zero, were found to be 4.1+\\/-0.2 kTc for indium, 3.6+\\/-0.2 kTc for tin, 4.6+\\/-0.2
P. L. Richards; M. Tinkham
Phonon-induced enhancements of the energy gap and critical current in superconducting aluminum
8 to 10 GHz phonons were generated by piezoelectric transduction of a microwave and by means of a quartz delay line, were allowed to enter the aluminum only after the microwaves had long since disappeared. The maximum enhancements detected were (deltaT/T/sub c/) = -0.07, for i/sub c/ and (deltaT/T/sub c/) = -0.03 for ..delta... The power- and temperature-dependence (0.82 less than or equal to T/T/sub c/ less than or equal to 0.994) of the enhancements were compared with the prediction of a theory given by Eliashberg. The gap-enhancement was in good agreement with the theory only for low input lower. The critical current measurements are predicted to be in rough agreement with the ..delta.. measurements but this was not observed. The magnitude of the critical current enhancements was typically more than twice the observed gap enhancements. The measured critical current enhancement was relatively independent of temperature whereas the gap enhancement decreased rapidly as the temperature was lowered.
Seligson, D.
The soft superconducting gap in semiconductor Majorana nanowires
We theoretically consider the mysterious topic of the soft gap in the tunneling conductance of the proximity-induced superconductivity in a semiconductor-superconductor hybrid structure, where the observation of a zero-bias conductance peak has created considerable excitement because of its possible connection with the elusive zero-energy Majorana mode. The observed experimental superconducting tunneling gap in the semiconductor nanowire looks v-shaped with considerable subgap conductance even at very low temperatures in sharp contrast to the theoretically expected hard BCS gap with exponentially suppressed subgap conductance. We systematically study, by solving the appropriate BdG equations both numerically and analytically, a number of physical mechanisms (e.g. magnetic and non-magnetic disorder, finite temperature, dissipative Cooper pair breaking, interface fluctuations), which could, in principle, lead to a soft gap, finding that only the interface fluctuation effect is a quantitatively and qualitatively viable mechanism that is consistent with the experimental observations. Our work indicates that improving the quality of the superconductor-semiconductor interface would go a long way in enhancing the gap in the hybrid structures being used for studying the Majorana mode.
Takei, So; Fregoso, Benjamin M.; Hui, Hoi-Yin; Lobos, Alejandro M.; Das Sarma, Sankar
Transient Increase of the Energy Gap of Superconducting NbN Thin Films Excited by Resonant Narrow-Band Terahertz Pulses
Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2?/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2?/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale.
Beck, M.; Rousseau, I.; Klammer, M.; Leiderer, P.; Mittendorff, M.; Winnerl, S.; Helm, M.; Gol'tsman, G. N.; Demsar, J.
Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses.
Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2?/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2?/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100Āps time scale. PMID:23848912
Beck, M; Rousseau, I; Klammer, M; Leiderer, P; Mittendorff, M; Winnerl, S; Helm, M; Gol'tsman, G N; Demsar, J
Numerical calculations of the spin polarized superconducting gap equation
Discovery of coexistence of superconductivity with weak feromagnetism in metals such as URhGe and ZrZn2 has led to renewed interest in the microscopic theory of such systems. We have developed a method to numerically solve the spin polarized Bogoliubov - de Gennes (BdG) superconducting gap equation for arbitrary Fermi surfaces. These solutions are then used to investigate the affects of the shape of various Fermi surfaces on non-zero momentum singlet Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing. The selfconsistent BdG gap equation is derived from a Hamiltonian that includes a Zeeman splitting term as well as the standard kinetic energy and a singlet pairing potential. Since we are numerically solving the gap equation, we can work with arbitrary dispersion relationships and multiple bands. These dispersion relationships can be taken from electronic structure calculations or from some analytic model. For a given exchange splitting and gap, the optimum pair momentum and pairing potential is found. Calculations for a number of Fermi surfaces illustrate how the shape of the Fermi surface (viz. flat portions) affects the tendency to form FFLO states.
Kyker, Alan; Pickett, Warren; Gygi, Francois
Stoner gap in the superconducting ferromagnet U Ge2
We report the temperature (T) dependence of ferromagnetic Bragg peak intensities and dc magnetization of the superconducting ferromagnet UGe2 under pressure (P) . We have found that the low- T behavior of the uniform magnetization can be explained by a conventional Stoner model. A functional analysis of the data produces the following results: The ferromagnetic state below a critical pressure can be understood as the perfectly polarized state, in which heavy quasiparticles occupy only majority spin bands. A Stoner gap ?(P) decreases monotonically with increasing pressure and increases linearly with magnetic field. We show that the present analysis based on the Stoner model is justified by a consistency check, i.e., comparison of density of states at the Fermi energy deduced from the analysis with observed electronic specific heat coefficients. We also argue the influence of the ferromagnetism on the superconductivity.
Aso, N.; Motoyama, G.; Uwatoko, Y.; Ban, S.; Nakamura, S.; Nishioka, T.; Homma, Y.; Shiokawa, Y.; Hirota, K.; Sato, N. K.
Heat Transport as a Probe of Superconducting Gap Structure
The structure of the superconducting gap provides important clues on the symmetry of the order parameter and the pairing mechanism. The presence of nodes in the gap function imposed by symmetry implies an unconventional order parameter, other than s-wave. Here we show how measurements of the thermal conductivity at very low temperature can be used to determine whether such nodes are present in a particular superconductor, and shed light on their nature and location. We focus on the residual linear term at T {yields} 0. A finite value in zero magnetic field is strong evidence for symmetry-imposed nodes, and the dependence on impurity scattering can distinguish between a line of nodes or point nodes. Application of a magnetic field probes the low-energy quasiparticle excitations, whether associated with nodes or with a small value of the gap on some part of the Fermi surface, as in a multi-band superconductor. We frame our discussion around archetypal materials: Nb for s-wave, Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} for d-wave, Sr{sub 2}RuO{sub 4} for p-wave, and NbSe{sub 2} for multi-band superconductivity. In that framework, we discuss three heavy-fermion superconductors: CeIrIn{sub 5}, CeCoIn{sub 5} and UPt{sub 3}.
Petrovic, C.; Shakeripour, H.; Taillefer, L.
Abrupt change in the energy gap of superconducting Ba1-xKxFe2As2 single crystals with hole doping
We performed a laser angle-resolved photoemission spectroscopy (ARPES) study on a wide doping range of Ba1-xKxFe2As2 (BaK) and precisely determined the doping evolution of the superconducting gaps in this compound. The gap size of the outer hole Fermi-surface (FS) sheet around the Brillouin zone (BZ) center shows an abrupt drop with overdoping (for x? 0.6) while the inner and middle FS gaps roughly scale with Tc. This is accompanied by the simultaneous disappearance of the electron FS sheet with similar orbital character at the BZ corner. These results indicate the different contributions of X2-Y2 and XZ/YZ orbitals to superconductivity in BaK and can hardly be completely reproduced by the available theories on iron-based superconductors.
Malaeb, W.; Shimojima, T.; Ishida, Y.; Okazaki, K.; Ota, Y.; Ohgushi, K.; Kihou, K.; Saito, T.; Lee, C. H.; Ishida, S.; Nakajima, M.; Uchida, S.; Fukazawa, H.; Kohori, Y.; Iyo, A.; Eisaki, H.; Chen, C.-T.; Watanabe, S.; Ikeda, H.; Shin, S.
Superconducting energy gap and normal state conductivity of a single domain Y sub 1 Ba sub 2 Cu sub 3 O sub 7 crystal
Using polarized reflectivity measurements of single domain crystals, we are able to distinguish chain and plane contributions to the infrared conductivity of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7}. A substantial chain contribution to {sigma}({omega}) persisting to low frequency and temperature is observed. For the intrinsic conductivity of the CuO{sub 2} planes a superconducting energy gap of 500 cm{sup {minus}1} (2{Delta}/k{Tc} {approx equal} 8) is evident in the infrared data, while the normal state conductivity drops much more slowly with {omega} than the ordinary Drude form, and can be described in terms of a scattering rate {Dirac h}/{tau}* {approximately} kT + {Dirac h}{omega} at low frequency. The former result (2{Delta}/k{Tc} {approx equal} 8) suggests substantial suppression of {Tc}; the latter, that Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} is not ordinary Fermi liquid. 26 refs., 4 figs.
Schlesinger, Z.; Collins, R.T.; Holtzberg, F.; Feild, C.; Blanton, S.H. (International Business Machines Corp., Yorktown Heights, NY (USA). Thomas J. Watson Research Center); Welp, U. (Science and Technology Center for Superconductivity (USA) Argonne National Lab., IL (USA)); Crabtree, G.W.; Fang, Y. (Argonne National Lab., IL (USA)); Liu, J.Z. (California Univ., Davis, CA (USA). Dept. of Physics)
Upper critical field, superconducting energy gaps and the Seebeck coefficient in La(0.8)Th(0.2)FeAsO.
We report the synthesis and characterization of a new electron-doped La-oxypnictide superconductor by partial substitution of lanthanum by thorium. The superconducting transition temperature at about 30.3ĀK was observed in La(0.8)Th(0.2)FeAsO, which is the highest in La-based oxypnictide superconductors synthesized at ambient pressure. We find that the decrease in lattice parameters with Th doping in LaOFeAs is more drastic as compared to that obtained by high pressure (6ĀGPa) synthesis of oxygen-deficient LaOFeAs. The resistivity and magnetic susceptibility measurements yield an upper critical field H(c2)(0) of 47ĀT. Partial substitution of Th in place of La induces electron doping, as shown by a negative Seebeck coefficient. The temperature-dependent magnetic penetration depth data provides strong evidence for a nodeless low energy gap of 1.4ĀmeV. PMID:21825433
Prakash, J; Singh, S J; Patnaik, S; Ganguli, A K
Triple-gap superconductivity of MgB2-(La,Sr)MnO3 composite
The interplay of superconductivity and magnetism was studied in a composite prepared from ferromagnetic half-metallic La0.67Sr0.33MnO3 (LSMO) nanoparticles and the s-wave superconductor MgB2. A few principal effects have been found. With the onset of MgB2 superconductivity, a spectacular drop of the sample resistance was detected and complete superconductivity was observed at temperatures up to 20 K. The basic nanocomposite characteristics (critical temperature, current-voltage dependence, percolation threshold, etc.) are strongly affected by the half-metallic LSMO and, most probably, cannot be quantitatively explained within the framework of a conventional percolation scenario. Point contact (PC) spectroscopy was used to measure directly the superconducting energy coupling. For small voltage, an excess current and doubling of the PC normal-state conductance were detected. Conductance peaks corresponding to three energy gaps are clearly observed. Two of these gaps we identified as enhanced ?? and ?? gaps originating from the MgB2; the third gap ?tr is more than three times larger than the largest MgB2 gap. The temperature behavior of ?tr does not follow the BCS dependence. The experimental results have a natural and qualitative explanation within the phase-coherency scenario of proximity-induced superconductivity. Specifically, at low temperature, a p-wave spin-triplet condensate with pairing energy ?tr is essentially sustained in LSMO but is incapable of displaying a long-range superconducting response because of a phase-disordered state. The proximity coupling to MgB2 restores the long-range phase coherency of the superconducting state, which, in turn, enhances the superconducting state of the MgB2.
Krivoruchko, V. N.; Tarenkov, V. Yu.
Relation between the nodal and antinodal gap and critical temperature in superconducting Bi2212
PubMed Central
An energy gap is, in principle, a dominant parameter in superconductivity. However, this view has been challenged for the case of high-Tc cuprates, because anisotropic evolution of a d-wave-like superconducting gap with underdoping has been difficult to formulate along with a critical temperature Tc. Here we show that a nodal-gap energy 2?N closely follows 8.5 kBTc with underdoping and is also proportional to the product of an antinodal gap energy ?* and a square-root superfluid density ?Ps for Bi2Sr2CaCu2O8+?, using low-energy synchrotron-radiation angle-resolved photoemission. The quantitative relations imply that the distinction between the nodal and antinodal gaps stems from the separation of the condensation and formation of electron pairs, and that the nodal-gap suppression represents the substantial phase incoherence inherent in a strong-coupling superconducting state. These simple gap-based formulae reasonably describe a crucial part of the unconventional mechanism governing Tc.
Anzai, H.; Ino, A.; Arita, M.; Namatame, H.; Taniguchi, M.; Ishikado, M.; Fujita, K.; Ishida, S.; Uchida, S.
Relation between the nodal and antinodal gap and critical temperature in superconducting Bi2212.
An energy gap is, in principle, a dominant parameter in superconductivity. However, this view has been challenged for the case of high-Tc cuprates, because anisotropic evolution of a d-wave-like superconducting gap with underdoping has been difficult to formulate along with a critical temperature Tc. Here we show that a nodal-gap energy 2?N closely follows 8.5 kBTc with underdoping and is also proportional to the product of an antinodal gap energy ?(*) and a square-root superfluid density ?Ps for Bi?Sr?CaCu?O?+?, using low-energy synchrotron-radiation angle-resolved photoemission. The quantitative relations imply that the distinction between the nodal and antinodal gaps stems from the separation of the condensation and formation of electron pairs, and that the nodal-gap suppression represents the substantial phase incoherence inherent in a strong-coupling superconducting state. These simple gap-based formulae reasonably describe a crucial part of the unconventional mechanism governing Tc. PMID:23652003
Anzai, H; Ino, A; Arita, M; Namatame, H; Taniguchi, M; Ishikado, M; Fujita, K; Ishida, S; Uchida, S
Optical investigations of the superconducting energy gap in b00-(BEDT-TTF)2SF5CH2CF2SO3
The organic salt {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} is a two-dimensional metal with a quarter-filled conduction band. In the metallic state the optical conductivity evidences interaction of the charge carriers with charge-order fluctuations that become stronger as temperature decreases. In the superconducting phase below T{sub c} {approx} 5K, indications of the superconducting gap with 2{Delta} {approx} 12 cm{sup -1} are observed in the optical spectrum, corresponding to 2{Delta}/k{sub B}T{sub c} {approx} 3.3. Its temperature and magnetic field dependences are also consistent with predictions by the BCS theory of a weakly coupled superconductor. The conductivity ratio {sigma}{sub 1}(T = 1.75 K)/{sigma}{sub 1}(10 K) indicates the opening of the superconducting gap in {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}.
Kaiser, S.; Yasin, S.; Drichko, N.; Dressel, M.; Room, T.; Huvonen, D.; Nagel, U.; Gard, G. L.; Schlueter, J. A. (Materials Science Division); (Universitat Stuttgart); (Nat. Inst. Chem. Phys. Biophys.); (Portland State Univ.)
Measurement of an enhanced superconducting phase and a pronounced anisotropy of the energy gap of a strained FeSe single layer in FeSe/Nb:SrTiO3/KTaO3 heterostructures using photoemission spectroscopy.
Single-layer FeSe films with an extremely expanded in-plane lattice constant of 3.99▒0.02??┼ are fabricated by epitaxially growing FeSe/Nb:SrTiO3/KTaO3 heterostructures and studied by inĀsitu angle-resolved photoemission spectroscopy. Two elliptical electron pockets at the Brillouin zone corner are resolved with negligible hybridization between them, indicating that the symmetry of the low-energy electronic structure remains intact as a freestanding single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70ĀK for the iron-based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results place strong constraints on current theories. PMID:24679321
Peng, R; Shen, X P; Xie, X; Xu, H C; Tan, S Y; Xia, M; Zhang, T; Cao, H Y; Gong, X G; Hu, J P; Xie, B P; Feng, D L
Effects of Energy GAP Anisotropy in Pure Superconductors.
Various effects of anisotropy of the superconducting energy gap are theoretically considered. In order to estimate the effects of anisotropy upon the thermodynamic properties of pure, single-crystal superconductors, a factorable BCS-like model for the eff...
J. R. Clem
Orbital-independent superconducting gaps in iron pnictides.
The origin of superconductivity in the iron pnictides has been attributed to antiferromagnetic spin ordering that occurs in close combination with a structural transition, but there are also proposals that link superconductivity to orbital ordering. We used bulk-sensitive laser angle-resolved photoemission spectroscopy on BaFe(2)(As(0.65)P(0.35))(2) and Ba(0.6)K(0.4)Fe(2)As(2) to elucidate the role of orbital degrees of freedom on the electron-pairing mechanism. In strong contrast to previous studies, an orbital-independent superconducting gap magnitude was found for the hole Fermi surfaces. Our result is not expected from the superconductivity associated with spin fluctuations and nesting, but it could be better explained invoking magnetism-induced interorbital pairing, orbital fluctuations, or a combination of orbital and spin fluctuations. Regardless of the interpretation, our results impose severe constraints on theories of iron pnictides. PMID:21474714
Shimojima, T; Sakaguchi, F; Ishizaka, K; Ishida, Y; Kiss, T; Okawa, M; Togashi, T; Chen, C-T; Watanabe, S; Arita, M; Shimada, K; Namatame, H; Taniguchi, M; Ohgushi, K; Kasahara, S; Terashima, T; Shibauchi, T; Matsuda, Y; Chainani, A; Shin, S
Fermi surfaces and energy gaps of high-temperature superconductors
In this short paper, we describe our recent experimental results from high-temperature superconductors. In the normal state, the data reveals interesting features of the Fermi surfaces and low energy excitations near the Fermi level. In the superconducting state, the data shows a very strong anisotropy in the superconducting gap.
Zhi-Xun Shen; Daniel S. Dessau
Bulk superconductivity and fully gapped superconducting state in Ba-doped phenanthrene
The superconducting state of Ba-intercalated phenanthrene, Ba1.5phenanthrene, has been investigated by specific-heat measurements down to 0.4 K. A clear anomaly associated with the superconducting transition at Tc=4.7 K indicates the bulk nature of the superconductivity. The temperature and the magnetic-field dependence of the electronic specific heat are consistent with a fully gapped superconducting order parameter. The electron-phonon coupling constant estimated from the specific-heat jump is 0.55 to 1.06, suggesting that the superconductivity of Ba1.5phenanthrene can be explained within the BCS approach with intermediate coupling mediated by phonons of approximately 100 cm-1 in frequency, which is assigned as intercalant phonons or intermolecular phonon modes.
Kasahara, Yuichi; Takeuchi, Yuki; Iwasa, Yoshihiro
Theoretical analysis of two-gap superconductivity of magnesium diborades and iron pnictides in the generalized {alpha} model
A generalized {alpha} model for computing the superconducting parameters of real two-band superconductors is proposed based on an analysis of the properties of two-band equations in the theory of superconductivity. Using this model, we calculate the heat capacity and optical properties of Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} superconducting compound and obtain the temperature dependences of the gaps and energies of the Leggett modes in the Mg{sub 1-x}Al{sub x}B{sub 2} superconducting system. Good quantitative coincidence of the calculated data and experimental results is demonstrated.
Maksimov, E. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Karakozov, A. E., E-mail: email@example.com [Russian Academy of Sciences, Vereshchagin Institute for High-Pressure Physics (Russian Federation); Gorshunov, B. P., E-mail: email@example.com [Russian Academy of Sciences, Prokhorov Institute of General Physics (Russian Federation); Ponomarev, Ya. G. [Moscow State University (Russian Federation); Zhukova, E. S. [Russian Academy of Sciences, Prokhorov Institute of General Physics (Russian Federation); Dressel, M. [Universitaet Stuttgart, 1. Physikalisches Institut (Germany)
The critical temperature and gap solution in the Bardeen-Cooper-Schrieffer theory of superconductivity
The Letter studies the problem of numerical approximations of the critical transition temperature and the energy gap function in the Bardeen-Cooper-Schrieffer equation arising in superconductivity theory. The positive kernel function leads to a phonon-dominant state at zero temperature. Much attention is paid to the equation defined on a bounded region. Two discretized versions of the equation are introduced. The first
Qiang Du; Yisong Yang
Raman Scattering by Superconducting-Gap Excitations and Their Coupling to Charge-Density Waves
2H-NbSe2 undergoes a charge-density-wave (CDW) distortion at 33 K which induces A and E Raman-active phonon modes. These are joined in the superconducting state at 2 K by new A and E Raman modes close in energy to the BCS gap 2Delta. Magnetic fields suppress the intensity of the new modes and enhance that of the CDW-induced modes, thus providing
R. Sooryakumar; M. V. Klein
In-gap states of a quantum dot coupled between a normal and a superconducting lead.
We study the in-gap states of a quantum dot hybridized with one conducting and another superconducting electrode. The proximity effect suppresses the electronic states in the entire subgap regime |?| < ?, where ? denotes the energy gap of the superconductor. The Andreev scattering mechanism can induce, however, some in-gap states whose line-broadening (inverse life-time) is controlled by the hybridization of the quantum dot with the normal electrode. We show that the number of such Andreev bound states is substantially dependent on the competition between the Coulomb repulsion and the induced on-dot pairing. We discuss the signatures of these in-gap states in the tunneling conductance, especially in a low-bias regime. PMID:24107469
Bara?ski, J; Doma?ski, T
Superconducting magnetic energy storage
Recent programmatic developments in Superconducting Magnetic Energy Storage (SMES) have prompted renewed and widespread interest in this field. In mid 1987 the Defense Nuclear Agency, acting for the Strategic Defense Initiative Office, issued a request for proposals for the design and construction of SMES Engineering Test Model (ETM). Two teams, one led by Bechtel and the other by Ebasco, are now engaged in the first phase of the development of a 10 to 20 MWhr ETM. This report presents the rationale for energy storage on utility systems, describes the general technology of SMES, and explains the chronological development of the technology. The present ETM program is outlined; details of the two projects for ETM development are described in other papers in these proceedings. The impact of high T/sub c/ materials on SMES is discussed. 69 refs., 3 figs., 3 tabs.
Hassenzahl, W.
Energy gaps in ?-graphdiyne nanoribbons
?-graphdiyne is a novel predicted Dirac cone material, which is similar to graphene. But the absence of a band gap significantly limits its practical applications. In order to extend this limitation, an opening of energy gap is needed. To this end, we resort to the nanoribbon structure of ?-graphdiyne. This is a conventional proposal to open up the energy gaps in nanomaterials. The results show that both the armchair and the zigzag ?-graphdiyne nanoribbons do generate energy gaps, which are width-dependent. In addition, the underlying mechanism of this opening is explored. The former is ascribed to the combination of quantum confinement and edges' effect, while the latter arises from the edge magnetic ordering. These novel nanoribbons with opening energy gaps would be potentially used in electronic devices.
Niu, X. N.; Yang, D. Z.; Si, M. S.; Xue, D. S.
Energy gap structure of layered superconductors
We report the energy gap structure and density-of-states (DOS) of a model layered superconductor with one superconducting layer and one normal layer in a unit cell along the c-axis. In the physically interesting parameter range where the interlayer hopping strengths of the quasiparticles are comparable to the critical temperature, the peaks in the DOS curve do not correspond to the order parameter (OP) of the superconducting layer, but depend on the OP and the band dispersion in the c-direction in a complex manner. In contrast to a BCS superconductor, the DOS of layered systems have logarithmic singularities. Our simulated tunneling characteristics bear close resemblance to experimental results.
Liu, S.H. [Oak Ridge National Lab., TN (United States); Klemm, R.A. [Argonne National Lab., IL (United States)
Design Tool for Liquid-Nitrogen Gaps in Superconducting Apparatus
For designers of high temperature superconducting equipment with liquid nitrogen as a dielectric, an expedient universal curve is sought that provides breakdown strength for a specified class of electrode shapes, with any practical sizes of electrodes and gap; thus the universal curve fills in missing experimental data. Universal breakdown strength curves at pressures of or slightly above 100 kPa, are being developed for AC, DC or impulse stress for the class with sphere-sphere, plane-plane and sphere-plane gaps, with three independent parameters: the size of each electrode and gap. A user can normalize his parameters and find the corresponding breakdown strength, even though no data were available for his exact dimensions. For AC and DC stresses the geometrical effects of stressed area/volume are incorporated from most published AC and DC experimental data of the last 50 years, by plotting breakdown field versus new geometrical quantities, such that all data fall approximately on or near one normalized universal curve. This avoids the usual difficult task of calculating stressed area and volume effects on the breakdown values for the graph ordinate. For impulse stress a more traditional plot suffices to produce a universal curve. This suggests that area/volume effects might not be so important with impulse stress. If the method proves reliable, it may be possible to determine design parameters for a broad range of geometries, help unify seemingly disparate breakdown data in the literature, and provide easily used, practical guidance for designers.
Pace, Marshall O [ORNL; Sauers, Isidor [ORNL; James, David Randy [ORNL; Tuncer, Enis [ORNL; Polyzos, Georgios [ORNL
Induced superconducting state and two-gap structure: Application to cuprate superconductors and conventional multilayers
An induced superconducting state caused by charge transfer between intrinsically superconducting (╬▒) and intrinsically normal (╬▓) subsystems is studied. A most interesting case is a layered system with some layers being normal. An analysis of the general Hamiltonian describing the phenomenon allows us to evaluate {ital T}{sub {ital c}} and the spectrum, which displays a two-gap structure. A superconducting state
Vladimir Kresin; Stuart Wolf
An induced superconducting state caused by charge transfer between intrinsically superconducting (alpha) and intrinsically normal (beta) subsystems is studied. A most interesting case is a layered system with some layers being normal. An analysis of the general Hamiltonian describing the phenomenon allows us to evaluate Tc and the spectrum, which displays a two-gap structure. A superconducting state can be induced
Vladimir Z. Kresin; Stuart A. Wolf
Two-Fermi-surface superconducting state and a nodal d-wave energy gap of the electron-doped Sm1.85Ce0.15CuO(4-?) cuprate superconductor.
We report on laser-excited angle-resolved photoemission spectroscopy in the electron-doped cuprate Sm1.85Ce0.15CuO(4-?). The data show the existence of a nodal hole-pocket Fermi surface both in the normal and superconducting states. We prove that its origin is long-range antiferromagnetism by an analysis of the coherence factors in the main and folded bands. This coexistence of long-range antiferrmagnetism and superconductivity implies that electron-doped cuprates are two-Fermi-surface superconductors. The measured superconducting gap in the nodal hole pocket is compatible with a d-wave symmetry. PMID:21668192
Santander-Syro, A F; Ikeda, M; Yoshida, T; Fujimori, A; Ishizaka, K; Okawa, M; Shin, S; Liang, B; Zimmers, A; Greene, R L; Bontemps, N
Far-infrared signature of the superconducting gap in intercalated graphite CaC6
Terahertz reflectance spectra of the Ca-intercalated graphite CaC6 reveal a superconducting gap below 11 K. The gap signature lacks a sharp onset to full reflectivity at 2?0 but rather shows a distribution of gap values consistent with an anisotropic gap. The experimental data were successfully fitted to the gap distribution obtained from density-functional calculations of Sanna [Phys. Rev. B 75, 020511(R) (2007)]. The temperature dependence of the superconducting gap is characteristic for a BCS type superconductor.
Nagel, U.; H³vonen, D.; Joon, E.; Kim, J. S.; Kremer, R. K.; R§§m, T.
Energy gaps in graphene nanoribbons.
Based on a first-principles approach, we present scaling rules for the band gaps of graphene nanoribbons (GNRs) as a function of their widths. The GNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen passivation. Both varieties of ribbons are shown to have band gaps. This differs from the results of simple tight-binding calculations or solutions of the Dirac's equation based on them. Our ab initio calculations show that the origin of energy gaps for GNRs with armchair shaped edges arises from both quantum confinement and the crucial effect of the edges. For GNRs with zigzag shaped edges, gaps appear because of a staggered sublattice potential on the hexagonal lattice due to edge magnetization. The rich gap structure for ribbons with armchair shaped edges is further obtained analytically including edge effects. These results reproduce our ab initio calculation results very well. PMID:17155765
Son, Young-Woo; Cohen, Marvin L; Louie, Steven G
Energy Gaps in Graphene Nanoribbons
Based on a first-principles approach, we present scaling rules for the band gaps of graphene nanoribbons (GNRs) as a function of their widths. The GNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen passivation. Both varieties of ribbons are shown to have band gaps. This differs from the results of simple tight-binding calculations or solutions of the DiracÆs equation based on them. Our ab initio calculations show that the origin of energy gaps for GNRs with armchair shaped edges arises from both quantum confinement and the crucial effect of the edges. For GNRs with zigzag shaped edges, gaps appear because of a staggered sublattice potential on the hexagonal lattice due to edge magnetization. The rich gap structure for ribbons with armchair shaped edges is further obtained analytically including edge effects. These results reproduce our ab initio calculation results very well.
Son, Young-Woo; Cohen, Marvin L.; Louie, Steven G.
First High power test results for 2.1 GHz superconducting photonic band gap accelerator cavities.
We report the results of the recent high power testing of superconducting radio frequency photonic band gap (PBG) accelerator cells. Tests of the two single-cell 2.1 GHz cavities were performed at both 4 and 2 K. An accelerating gradient of 15 MV/m and an unloaded quality factor Q(0) of 4ū10(9) were achieved. It has been long realized that PBG structures have great potential in reducing long-range wakefields in accelerators. A PBG structure confines the fundamental TM(01)-like accelerating mode, but does not support higher order modes. Employing PBG cavities to filter out higher order modes in superconducting particle accelerators will allow suppression of dangerous beam instabilities caused by wakefields and thus operation at higher frequencies and significantly higher beam luminosities. This may lead towards a completely new generation of colliders for high energy physics and energy recovery linacs for the free-electron lasers. PMID:23215084
Simakov, Evgenya I; Haynes, W Brian; Madrid, Michael A; Romero, Frank P; Tajima, Tsuyoshi; Tuzel, Walter M; Boulware, Chase H; Grimm, Terry L
Superconducting energy storage magnet
NASA Technical Reports Server (NTRS)
A superconducting magnet is formed having composite conductors arrayed in coils having turns which lie on a surface defining substantially a frustum of a cone. The conical angle with respect to the central axis is preferably selected such that the magnetic pressure on the coil at the widest portion of the cone is substantially zero. The magnet structure is adapted for use as an energy storage magnet mounted in an earthen trench or tunnel where the strength the surrounding soil is lower at the top of the trench or tunnel than at the bottom. The composite conductor may be formed having a ripple shape to minimize stresses during charge up and discharge and has a shape for each ripple selected such that the conductor undergoes a minimum amount of bending during the charge and discharge cycle. By minimizing bending, the working of the normal conductor in the composite conductor is minimized, thereby reducing the increase in resistance of the normal conductor that occurs over time as the conductor undergoes bending during numerous charge and discharge cycles.
Boom, Roger W. (Inventor); Eyssa, Yehia M. (Inventor); Abdelsalam, Mostafa K. (Inventor); Huang, Xianrui (Inventor)
Signatures of the s+ superconducting gap in electronic Raman Scattering and optical conductivity of Fe-based superconductors
We analyze the consequences of the extended s-wave symmetry of the superconducting gap, proposed recently in Fe-based superconductors, for the electronic pair-breaking Raman scattering and optical conductivity. We calculate conductivity and Raman intensity for elastic scattering and find that an extended s-wave superconducting gap gives rise to several specific features in optical and Raman response functions. In particular, we find that, for the A1g symmetry of the incoming light, there will be a resonant collective mode in the Raman response function at an energy ?<2?. The latter is as a hallmark of the s+ superconductivity. Furthermore, the Cooper-pair weakening due to strong inter-band impurity scattering shifts the 2? features towards higher energies in both Raman scattering and optical conductivity. We argue that these features are present in the experimental data for iron-based superconductors.
Eremin, Ilya; Chubukov, Andrey V.; Korshunov, Maxim M.
Observation of coherent superconducting gap excitations in MgB_2
We report the observation of coherent superconducting gap oscillations in MgB2 films at 3K using time-domain pump-probe spectroscopy. The Fourier spectrum shows peaks at 124cm -1 and 103cm-1 associated with gaps in the ? electron band, and a weaker feature at 56cm -1 associated with the ? band gap. Consistent with [1], spontaneous Raman spectra on the same sample shows a single peak at 110cm-1. The coherent superconducting gap oscillations and the Raman peak disappear above the transition temperature. [1]. J. W. Quilty, S. Lee, A. Yamamoto, and S. Tajima, Phys. Rev. Lett., 88, 87001 (2002).
Aku-Leh, C.; Eckhause, T. A.; Bragas, A. V.; Merlin, R.; Zeng, X. H.; Pogrebnyakov, A. V.; Tenne, D. A.; Xi, X. X.
Superconducting gap excitations, acoustic and optical phonons probed with femtosecond time-resolved and Raman spectroscopy
Spontaneous Raman scattering and femtosecond time-resolved pump-probe spectroscopy are used to study and characterize material properties in superconductors, bulk semiconductors and semiconducting quantum dots. Superconducting gap oscillations are observed for the first time in MgB 2 (Tc = 39 K) and 2H-NbSe2 ( Tc = 7 K). In MgB2, multiple superconducting gap oscillations are observed at 24 cm-1, 103 cm
Cynthia Aku-Leh
Far-infrared signature of a superconducting gap in intercalated graphite CaC6.
CaC6 is exceptional in the series of intercalated graphite compounds because of its high superconducting transition temperature, Tc=11.5K. The superconducting gap, 2?=25.6 ▒ 3.2cm-1, measured by scanning tunneling spectroscopy (N. Bergeal et al., PRL 97, 077003 (2006)), is consistent with the weak-coupling BCS type superconductivity. The superconducting gap can be directly probed also by far-infrared spectroscopy. We studied the reflectance R of CaC6 between 4 and 100cm-1 from 3K to 15K. We see the signature of the superconducting gap in the reflectance ratio of superconducting state Rs to the normal state Rn and can follow its temperature dependence. The appearance of the gap signature in Rs/Rn tells us that CaC6 is in the dirty limit. Different models, including an anisotropic gap and a multi-gap scenario, will be discussed to fit the optical data.
Nagel, U.; Huvonen, D.; Room, T.; Kim, J. S.; Boeri, L.; Kremer, R. K.; Razavi, F. S.
Wisconsin superconductive energy storage project
In 1970, research effort was initiated at the University of Wisconsin by two Engineering College faculty members to determine the merits of superconductive inductor energy storage units, called I-C (inductor-converter) units, for electric power systems. Interest in the project increased rapidly. The first research proposal was prepared in 1971. The first paper was presented in Kyoto, Japan, at INTERMAG in
H. A. Peterson; R. W. Boom; W. C. Young
Tunneling observation of the finite superconducting gap in YBa 2Cu 3O y
Electron tunneling study on YBa 2Cu 3O y was carried out for investigation of an essential superconducting gap structure. Besides usual NIS junction, a kind of micro-break SIS junction was prepared in-situ on a low-temperature scanning tunneling microscope/spectroscope (LT-STM/STS) stage in order to minimize the influence of the surface-degradation. As the result, the observed tunneling spectra showed finite superconducting gap structure with extremely low and flat in-gap density of states, which indicates a quite different character from the gapless one expected by the d-wave pairing theory.
Murakami, Hironaru; Ohbuchi, Syuzo; Aoki, Ryozo
Doping - dependent anisotropy of the superconducting gap in underdoped pnictide superconductors
The in-plane London penetration depth, ??(T), was studied in single crystals of Ba1-xKxFe2As2 (``Ba122") and Ca10(Pt3As8)[(Fe1-xPtx)2As2]5 (``10-3-8"). Whereas in Ba122 magnetism and superconductivity coexist in the underdoped regime, the 10-3-8 compound exhibits a clear separation of two order parameters. By comparing the results obtained in these two systems, we could study general features of the superconducting gap structure as function of doping in the underdoped regime. Similar to all other pnictides, the low-temperature variation of London penetration depth exhibits a power-law behavior, ??(T)= AT^n, in both systems. Moving towards the underdoped edge of the superconducting dome, the exponent n decreases well below scattering - limited value of n=2 and, at the same time, the pre-factor A increases. Both trends indicate an increasing anisotropy of the superconducting gap in more underdoped compounds. These and previous results suggest that the development of the superconducting gap anisotropy towards the underdoped edge of the superconducting dome is an intrinsic property of iron pnictides, similar to the known tendency on the overdoped side where magnetism and superconductivity do not interfere.[4pt] In collboration with M.A. Tanatar, H. Kim, The Ames Laboratory; Bing Shen, Hai-Hu Wen, Nanjing University; and N. Ni, R.J. Cava, Princeton University.
Prozorov, Ruslan
Superconducting Magnetic Energy Storage (SMES) Program
A 30 MJ superconducting magnetic energy storage (SMES) unit to stabilize power oscillations was developed. The 30 MJ superconducting coil manufacture is completed and the design of the seismic mounting of the coil to the nonconducting dewar lid and a concrete foundation is complete. An economic and technological evaluation of superconducting fault current limiter (SFCL) was completed and the results are reported.
Rogers, J. D.
Fusion power production requires energy storage and transfer on short time scales to create confining magnetic fields and for heating plasmas. The theta pinch Scyllac Fusion Test Reactor (SFTR) requires 480 MJ of energy to drive the 5-T compression field with a 0.7-ms rise time. Tokamak Experimental Power Reactors (EPR) require 1 to 2 GJ of energy with a 1
J. D. Rogers
Signature of superconductivity in UBe13 as seen by neutron scattering: Superconducting and magnetic energy scales
We here present inelastic neutron scattering results on the strongly correlated cubic superconductor UBe13 (Tc = 0.85 K) obtained on a large single crystal by high-resolution cold neutron three-axis spectroscopy. We observed spin dynamics at a unique momentum space position building up below T ś50 K and changing significantly on entering the superconducting state. The observed short-range longitudinal character of the correlations can be understood as a result of competing magnetic interactions. The energy dependence in the normal state reflects the energy scales determined from specific heat, whereas the low-temperature data suggest the opening of a superconducting gap. Our findings are consistent with a superconducting order parameter exhibiting s ▒ or d-wave symmetry and placing pure UBe13 in the strong coupling regime.
Hiess, A.; Schneidewind, A.; Stockert, O.; Fisk, Z.
Non-Fermi liquid behavior and non-universal superconducting gap structure in Fe-pnictides
The discovery of Fe-pnictide superconductors with Tc exceeding 55 K raises fundamental questions about origin of high-Tc superconductivity. Here we report the systematic studies of the normal-state charge transport, Fermi surface structure and superconducting gap structure in high-quality single crystals of BaFe2(As1-xPx)2 (0 <=x <=0.71), ranging from the SDW state to overdoped Fermi liquid state. Near the SDW boundary, the
Yuji Matsuda
Derivation of the superconducting gap equation for the noncentrosymmetric superconductor Li2Pt3B
We present here the mathematical background of our approach, presented in [1] regarding the gap function and symmetry for the noncentrosymmetric (NCS) superconductor Li2Pt3B. As revealed by the experiment, this NCS superconductor gives rise to line nodes in the superconducting order parameter, which is responsible for many of its experimental behaviors. Owing to the enhanced d-character of the relevant bands that cross the Fermi level, the system gets weakly correlated. The nature and symmetry of this nodal behavior is explained from a microscopic viewpoint. In this article starting with an Hubbard model relevant for this NCS system by considering the effect of the onsite Coulomb repulsion on the pairing potential perturbatively, we extract the superconducting gap equation. Further analysis [1] of this equation predicts a s+/- wave gap function with line nodes as the most promising candidate in the superconducting state.
Mukherjee, Soumya P.; Takimoto, Tetsuya
Theory of extracting superconducting gap structure from field-angle rotational experiments
We study the relation between the superconducting gap structure and field-orientational dependence of zero-energy density of states (ZEDOS), on the basis of an approximate analytical solution of the Eilenberger equation. Firstly, we quantitatively estimate the crossover magnetic field below which the result of the Doppler-shift method becomes correct. Secondly, we show that field-orientational dependence of ZEDOS has rather broad minima when the shape of node is point-like, in contrast to the result of the Doppler-shift method. Finally, we propose a novel mechanism leading to the cusp-like minima found in YNi2B2C in terms of a two-band model. This two-band model also provides a typical example in which the Doppler-shift predominant region is suppressed to much lower fields.
Udagawa, Masafumi; Yanase, Youichi; Ogata, Masao
Part I. Phenomenological Theories of Suoerconductivity: 1. Introduction; 2. The London-London equation; 3. Pippard's equation; 4. Thermodynamics of type I superconductor; 5. The intermediate state; 6. Surface energy between a normal and a superconducting metal; 7. Quantized vorticity; 8. Type II superconductivity; 9. The Ginzburg-Landau theory; 10. The upper critical field of a type II superconductor; 11. The anisotropic superconductor; 12. Superconductivity in thin slabs; 13. Surface superconductivity; 14. The type II superconductor for H just below Hc2; 15. The Josephson effect; 16. The Josephson lattice in 1D; 17. Vortex structures in layered superconductors; 18. Granular superconductors; the Josephson lattice in 2D and 3D; 19. Wave propagation in Josephson junctions, superlattices and arrays; 20. Flux pinning and flux motion; 21. Time dependent Ginzburg-Landau theory; 22. Fluctuation effects; 23. Ginzburg-Landau theory of an unconventional superfluid; 24. Landau Fermi liquid theory; Part II. The Microscopic Theory of a Uniform Superconductor: 25. The Cooper problem: pairing of two electrons above a filled Fermi sea; 26. The Bardeen-Cooper-Schrieffer theory of the superconducting ground state; 27. Elementary excitations; the Bogoliubov-Valatin transformation; 28. Calculation of the thermodynamic properties using the Bogoliubov-Valatin method; 29. Quasiparticle tunneling; 30. Pair tunneling: the microscopic theory of the Josephson effects; 31. Simplified discussion of pairing mechanisms; 32. The effect of Coulomb repulsion on Tc; 33. The two band superconductor; 34. Time dependent perturbations; 35. Non equilibrium superconductivity; Part III. Non Uniform Superconductors: 36. Bogoliubov's self-consistent potential equations; 37. Self consistency conditions and the free energy; 38. Linearized self consistency and the correlation function; 39. Behaviour of the correlation function in the clean and dirty limits; 40. Self consistency condition; 41. Effects involving electron spin; 42. Boundary conditions; 43. The proximity effect at zero field; 44. Proximity effect in a magnetic field; 45. Derivation of the Ginzburg-Landau theory; 46. Gauge invariance; Diamagnetism in the low field limit; 47. The quasi-classical case; 48. The isolated vortex line; 49. Time dependent Bogoliubov equations; 50. The response of a superconductor to an electromagnetic field; 51. The Bogoliubov equations for an unconventional superfluid; 53. Superfluid 3He; 54. Collective modes in normal and superfluid Fermi systems; 55. Green's functions; Appendix A. The occupation number representation; Appendix B. Some calculations involving the BCS wavefunction; Appendix C. The gap as a perturbation through third order; References; Additional reading; List of mathematical and physical symbols; Index.
Ketterson, J. B.; Song, S. N.
Possible Multiple Gap Superconductivity with Line Nodes in Heavily Hole-Doped Superconductor KFe2As2 Studied by 75As Nuclear Quadrupole Resonance and Specific Heat
We report the 75As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe2As2 (superconducting transition temperature Tc? 3.5 K). The spin-lattice relaxation rate 1/T1 in the superconducting state exhibits a gradual temperature dependence with no coherence peak below Tc. The quasiparticle specific heat CQP/T shows a small jump, which is about 30% of the electronic specific heat coefficient just below Tc. The CQP/T suggests the existence of low-energy quasiparticle excitation at the lowest measurement temperature T=0.4 K? Tc/10. The T dependences of 1/T1 and CQP/T can be explained by a multiple nodal superconducting gap scenario rather than by a multiple fully gapped s▒-wave scenario determined using simple gap analysis.
Fukazawa, Hideto; Yamada, Yuji; Kondo, Kenji; Saito, Taku; Kohori, Yoh; Kuga, Kentarou; Matsumoto, Yosuke; Nakatsuji, Satoru; Kito, Hijiri; Shirage, Parasharam M.; Kihou, Kunihiro; Takeshita, Nao; Lee, Chul-Ho; Iyo, Akira; Eisaki, Hiroshi
Testing the sign-changing superconducting gap in iron-based superconductors with quasiparticle interference and neutron scattering.
We present a phenomenological calculation of the quasiparticle interference (QPI) pattern and inelastic neutron scattering (INS) spectra in iron-pnictide and layered iron-selenide compounds by using material specific band structure and superconducting (SC) gap properties. As both the QPI and the INS spectra arise due to scattering of the Bogolyubov quasiparticles, they exhibit a one-to-one correspondence of the scattering vectors and the energy scales. We show that these two spectroscopies complement each other in such a way that a comparative study allows one to extract quantitative and unambiguous information about the underlying pairing structure and the phase of the SC gap. Due to the nodeless and isotropic nature of the SC gaps, both the QPI and INS maps are concentrated at only two energies in pnictide (two SC gaps) and one energy in iron-selenide, while the associated scattering vectors q for scattering of sign-changing and same sign of the SC gaps change between these spectroscopies. The results presented, particularly for the newly discovered iron-selenide compounds, can be used to test the nodeless d-wave pairing in this class of high temperature superconductor. PMID:22498771
Das, Tanmoy; Balatsky, A V
The discovery of Fe-pnictide superconductors with Tc exceeding 55 K raises fundamental questions about origin of high-Tc superconductivity. Here we report the systematic studies of the normal-state charge transport, Fermi surface structure and superconducting gap structure in high-quality single crystals of BaFe2(As1-xPx)2 (0 <=x <=0.71), ranging from the SDW state to overdoped Fermi liquid state. Near the SDW boundary, the transport coefficients, including resistivity, Hall coefficient and magnetoresistance, exhibit striking deviations from the Fermi liquid properties [1]. The Fermi surface structure determined by the dHvA effect shows that in the superconducting dome the volume of the electron and hole sheets shrink linearly and the effective masses become strongly enhanced with decreasing x [2]. It is likely that these trends originate from the many-body interaction which gives rise to superconductivity. The penetration depth, thermal conductivity and NMR data for BaFe2(As0.67P0.33)2 (Tc=30 K) provide unambiguous evidence for line nodes in the superconducting gap function [3], in sharp contrast to the other Fe-based compounds with fully gapped structure. This indicates that the gap structure of Fe-based high-Tc superconductors is not universal.[1] S. Kasahara et al., arXiv:0905.4427 [2] H. Shishido et al., arXiv:0910.3634 [3] K. Hashimoto et al., arXiv:0907.4399 [4] K. Hashimoto et al., Phys. Rev. Lett. 102, 017002 (2009), ibid 102, 207001 (2009).
Matsuda, Yuji
Neutron Diffraction Study on Stoner Gap in the Superconducting Ferromagnet UGe2
We report the neutron diffraction study on the temperature dependence of Bragg peak intensities (IB) in the superconducting ferromagnet UGe2. When the temperature is lowered, IB(T) steeply increases below a characteristic temperature (TX) in the ferromagnetic phase. We have found that it can be explained in terms of a simple Stoner model, and that the so-called Stoner gap ? decreases with increasing pressure and collapses to zero around a critical pressure (PXś 1.2 GPa) where the superconducting transtion temperature displays a maximum. We speculate that a transition from the paramagnetic to perfect polarized state takes place at TX and PX in heavy electron bands.
Aso, Naofumi; Motoyama, Gaku; Ban, Seiko; Homma, Yoshiya
Observation of the Crossover from Two-Gap to Single-Gap Superconductivity through Specific Heat Measurements in Neutron-Irradiated MgB{sub 2}
We report specific heat measurements on neutron-irradiated MgB{sub 2} samples, for which the critical temperature is lowered to 8.7 K, but the superconducting transition remains extremely sharp, indicative of a defect structure extremely homogeneous. Our results evidence the presence of two superconducting gaps in the temperature range above 21 K, while single-gap superconductivity is well established as a bulk property, not associated with local disorder fluctuations, when T{sub c} decreases to 11 K.
Putti, M.; Ferdeghini, C.; Manfrinetti, P.; Tarantini, C. [CNR-INFM-LAMIA and Dipartimento di Fisica, Universita di Genova, Via Dodecaneso 33, 16146 Genova (Italy); Affronte, M. [CNR-INFM-S3 and Dipartimento di Fisica, Universita di Modena e Reggio Emilia, Via G. Campi 213/A, I-41100 Modena (Italy); Lehmann, E. [Paul Scherrer Institut, CH-5232 Villigen (Switzerland)
Superconducting gap in LiFeAs from three-dimensional spin-fluctuation pairing calculations
The lack of nesting of the electron and hole Fermi-surface sheets in the Fe-based superconductor LiFeAs, with a critical temperature of 18 K, has led to questions as to whether the origin of superconductivity in this material might be different from other Fe-based superconductors. Both angle-resolved photoemission and quasiparticle interference experiments have reported fully gapped superconducting order parameters with significant anisotropy. The system is also of interest because relatively strong correlations seem to be responsible for significant renormalization of the hole bands. Here we present calculations of the superconducting gap and pairing in the random-phase approximation using Fermi surfaces derived from measured photoemission spectra. The qualitative features of the gaps obtained in these calculations are shown to be different from previous two-dimensional theoretical works and in good agreement with experiment on the main Fermi-surface pockets. We analyze the contributions to the pairing vertex thus obtained and show that the scattering processes between electron and hole pockets that are believed to dominate the pairing in other Fe-based superconductors continue to do so in LiFeAs despite the lack of nesting, leading to gaps with anisotropic s▒ structure. Some interesting differences relating to the enhanced dxy orbital content of the LiFeAs Fermi surface are noted.
Wang, Y.; Kreisel, A.; Zabolotnyy, V. B.; Borisenko, S. V.; B³chner, B.; Maier, T. A.; Hirschfeld, P. J.; Scalapino, D. J.
Superconductivity: Phenomenology
This document discusses first the following topics: (a) The superconducting transition temperature; (b) Zero resistivity; (c) The Meissner effect; (d) The isotope effect; (e) Microwave and optical properties; and (f) The superconducting energy gap. Part II of this document investigates the Ginzburg-Landau equations by discussing: (a) The coherence length; (b) The penetration depth; (c) Flux quantization; (d) Magnetic-field dependence of the energy gap; (e) Quantum interference phenomena; and (f) The Josephson effect.
Falicov, L.M.
Infrared and microwave spectra of an energy gap in high-temperature superconductors
The optical reflectivity and microwave conductivity are calculated for a metal that becomes superconducting below a transition temperature Tc. Electron-electron scattering on a nested Fermi surface with an isotropic weak-coupling energy gap is found to yield a reflectance at low frequencies that is compatible with measurements on superconducting YBa2Cu3O7 crystals. The computed microwave surface resistance Rs drops dramatically near Tc
C. T. Rieck; W. A. Little; J. Ruvalds; A. Virosztek
Doping dependence of the superconducting gap in Bi2Sr2CaCu2O8+?
Bi2Sr2CaCu2O8+? crystals with varying hole concentrations (0.12
superconducting gap [?(k)]. Electronic Raman scattering experiments that sample regions of the Fermi surface near the diagonal (B2g) and principal axes (B1g) of the Brillouin zone have been utilized. The frequency dependence of the Raman response function ?'' at low energies [?(k)] is found to be linear for B2g and cubic for B1g (Tsuperconducting gap is consistent with dx2-y2 symmetry, for slightly underdoped and overdoped crystals. Studies of the pair-breaking peak found in the B1g spectra demonstrate that the magnitude of the maximum gap (|?max|) decreases monotonically with increasing hole doping, for p>0.12. Based on the magnitude of the B1g renormalization, it is found that the number of quasiparticles participating in pairing increases monotonically with increased doping. On the other hand, the B2g spectra show a weak ``pair-breaking peak'' that follows a paraboliclike dependence on hole concentration, for 0.12
Hewitt, K. C.; Irwin, J. C.
Hewitt, K. C.; Irwin, J. C.
Raising gradient limitations in 2.1 GHz superconducting photonic band gap accelerator cavities
We report results from recent 2.1 GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1 GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4 K and below 2 K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.
Simakov, Evgenya I.; Arsenyev, Sergey A.; Brian Haynes, W.; Shchegolkov, Dmitry Yu.; Suvorova, Natalya A.; Tajima, Tsuyoshi; Boulware, Chase H.; Grimm, Terry L.
LETTER TO THE EDITOR: The polar-type density of states in a non-unitary odd-parity superconducting state with a gap with point nodes
It is shown that a density of states (DOS) proportional to the excitation energy, a so-called polar-like DOS, can arise in odd-parity states, with the superconducting gap vanishing at points even though the spin-orbit interaction for Cooper pairing is strong. Such gap structures are realized in the non-unitary states, F1u (1, i, 0), F1u (1, varepsilon, varepsilon2), and F2u (1, i, 0), classified by Volovik and Gorkov (1985 Sov. Phys.-JETP 61 843). This is due to the gap vanishing in a quadratic manner around a point on the Fermi surface.
Miyake, K.
Based on a first-principles approach, we present scaling rules for the band\\u000agaps of graphene nanoribbons (GNRs) as a function of their widths. The GNRs\\u000aconsidered have either armchair or zigzag shaped edges on both sides with\\u000ahydrogen passivation. Both varieties of ribbons are shown to have band gaps.\\u000aThis differs from the results of simple tight-binding calculations or solutions
Young-Woo Son; Marvin L. Cohen; Steven G. Louie
We report the neutron diffraction study on the temperature dependence of Bragg peak intensities (IB) in the superconducting ferromagnet UGe2. When the temperature is lowered, IB(T) steeply increases below a characteristic temperature (TX) in the ferromagnetic phase. We have found that it can be explained in terms of a simple Stoner model, and that the so-called Stoner gap delta decreases
Naofumi Aso; Gaku Motoyama; Seiko Ban; Yoshiya Homma
High speed superconducting flywheel system for energy storage
A prototype of a flywheel system with auto stable high temperature superconducting bearings was built and tested. The bearings offered good vertical and lateral stability. A metallic flywheel disk, ° 190 mm x 30 mm, was safely rotated at speeds up to 15000 rpm. The disk was driven by a 3 phase synchronous homopolar motor/generator. Maximum energy capacity was 3.8 Wh, maximum power was 1.5 KW. The dynamic behavior of the prototype was tested, characterized and evaluated with respect to axial and lateral stiffness, decay torques (bearing drag), vibrational modes and critical speeds. The bearings supports a maximum weight of 65 N at zero gap, axial and lateral stiffness at 1 mm gap were 440 N/cm and 130 N/cm, respectively. Spin down experiments were performed to investigate the energy efficiency of the system. The decay rate was found to depend upon background pressure in the vacuum chamber and upon the gap width in the bearing. At a background pressure of 5x10 -4 Torr, the coefficient of friction (drag-to-lift ratio) was measured to be 0.000009 at low speeds for 6 mm gap width in the bearing. Our results indicate that further refinement of this technology will allow operation of higly efficient superconducting flywheels in the kWh range.
Bornemann, H. J.; Urban, C.; Boegler, P.; Ritter, T.; Zaitsev, O.; Weber, K.; Rietschel, H.
Energy loss in spark gap switches
The paper reports on numerical study of the energy loss in spark gap switches. The operation of the switches is analyzed using the Braginsky model which allows calculation of the time dependence of the spark channel resistance. The Braginsky equation is solved simultaneously with generator circuit equations for different load types. Based on the numerical solutions, expressions which determine both the energy released in a spark gap switch and the switching time are derived.
Oreshkin, V. I.; Lavrinovich, I. V.
Evolution of superconducting gap and metallic ground state in cuprates from transport
We report on fundamental characteristics of the ground state of cuprates in the limit of T=0, for both normal and superconducting states, obtained from transport measurements on high-quality single crystals of YBCO and Tl-2201, as a function of hole concentration. The superconducting gap is extracted from thermal conductivity; it is found to scale with the superconducting transition temperature throughout the overdoped regime, with a gap-to-Tc ratio of 5 [1]. The normal state is accessed by suppressing superconductivity with magnetic fields up to 60 T and is characterized by the limiting behavior of its electrical resistivity; while carrier localization is observed in YBCO at low temperature for carrier concentrations p below 0.1 hole/planar Cu, at p=0.1 and above the material remains highly metallic down to T=0 [2]. This shows that the non-superconducting state of underdoped cuprates, deep in the pseudogap phase, is remarkably similar to that of strongly overdoped cuprates, e.g. at p=0.3. We compare these results with similar measurements on other cuprates and discuss their implication for our understanding of the cuprate phase diagram. [1] In collaboration with: D.G. Hawthorn, S.Y. Li, M. Sutherland, E. Boaknin, R.W. Hill, C. Proust, F. Ronning, M. Tanatar, J. Paglione, D. Peets, R. Liang, D.A. Bonn, W.N. Hardy, and N.N. Kolesnikov. [2] In collaboration with: C. Proust, M. Sutherland, N. Doiron- Leyraud, S.Y. Li, R. Liang, D.A. Bonn, W.N. Hardy, N.E. Hussey, S. Adachi, S. Tajima, J. Levallois, and M. Narbone.
Taillefer, Louis
Wisconsin superconductive energy storage project, volume 1
The initial feasibility and conceptual design study phase of superconductive energy storage project was completed. A thyristorized Graetz bridge converter, widely used and accepted by the power industry around the world, serves as the interface between the three phase power system and the energy storage inductor. The combination of inductor and converter permits energy to be taken out of the
R. W. Boom; H. A. Peterson; W. C. Young
Many potential high-temperature superconductivity (HTS) military applications have been demonstrated by low-temperature superconductivity systems; they encompass high efficiency electric drives for naval vessels, airborne electric generators, energy storage systems for directed-energy weapons, electromechanical launchers, magnetic and electromagnetic shields, and cavity resonators for microwave and mm-wave generation. Further HST applications in militarily relevant fields include EM sensors, IR focal plane arrays, SQUIDs, magnetic gradiometers, high-power sonar sources, and superconducting antennas and inertial navigation systems. The development of SQUID sensors will furnish novel magnetic anomaly detection methods for ASW.
Yeo, Yung K.
Spin-singlet superconductivity with a full gap in locally noncentrosymmetric SrPtAs
We report Pt-NMR195 and As75 nuclear quadrupole resonance measurements for the locally noncentrosymmetric superconductor SrPtAs where the As-Pt layer breaks inversion symmetry while globally the compound is centrosymmetric. The nuclear spin-lattice relaxation rate 1/T1 shows a well-defined coherence peak below Tc and decreases exponentially at low temperatures. The spin susceptibility measured by the Knight shift also decreases below Tc down to T superconducting state with a full gap. Our results suggest that the spin-orbit coupling due to the local inversion-symmetry breaking is not large enough to bring about an exotic superconducting state, or the interlayer hopping interaction is larger than the spin-orbit coupling.
Matano, K.; Arima, K.; Maeda, S.; Nishikubo, Y.; Kudo, K.; Nohara, M.; Zheng, Guo-qing
Antiferromagnetic and superconducting gaps and their interrelation in high-Tc cuprates
We propose a phenomenological model, comprising a microscopic SO(5) model plus the on-site Hubbard interaction U (projected SO(5) model) to understand the interrelation between the d-wave-gap modulation observed by recent angle-resolved photoemission experiments in the insulating antiferromagnet Ca2CuO2Cl2 and the d-wave gap of high-Tc superconducting materials. The on-site interaction U is important in order to produce a Mott gap of the correct order of magnitude, which would be absent in an exact SO(5) theory. The projected SO(5)-model explains the gap characteristics, namely both the symmetry and the different order of magnitude of the gap modulations between the AF and the SCc phases. Furthermore, it is shown that the projected SO(5) theory can provide an explanation for a recent observation [E. Pavarini et al., Phys. Rev. Lett. 87, 47003 (2001)], i. e. that the maximum Tc observed in a large variety of high-Tc cuprates scales with the next-nearest-neighbor hopping matrix element t.
Arrigoni, E.; Zacher, M. G.; Eckl, T.; Hanke, W.
Superconducting gap in the tunneling spectra of high-[Tc] cuprates
In Bi2212 and La214, the low-T (T [much lt] [Tc]) superconducting gap magnitude 2[Delta][sub 0] and the temperature dependence of in-plane resistivity [rho] were examined over a wide carrier-doping range. In both systems, 2[Delta][sub 0] increases with lowering doping level and [rho] starts decreasing faster around a temperature T[sup *], comparable to the mean-field [Tc] or the onset temperature of a spin-channel singlet formation in the mean-field RVB theory, each of which is given by [approximately][Delta][sub 0]/2[kappa][sub B].
Oda, M.; Hoya, K.; Abe, N.; Yokoyama, M.; Momono, N.; Nakano, T.; Nagata, T.; Ido, M. (Hokkaido Univ., Sapporo (Japan). Dept. of Physics)
High temperature superconducting magnetic energy storage for future NASA missions
Several NASA sponsored studies based on 'conventional' liquid helium temperature level superconductivity technology have concluded that superconducting magnetic energy storage has considerable potential for space applications. The advent of high temperature superconductivity (HTSC) may provide additional benefits over conventional superconductivity technology, making magnetic energy storage even more attractive. The proposed NASA space station is a possible candidate for the application of HTSC energy storage. Alternative energy storage technologies for this and other low Earth orbit missions are compared.
Faymon, Karl A.; Rudnick, Stanley J.
Superconducting gap in MgB(2): electronic Raman scattering measurements of single crystals.
Polarization-resolved Raman scattering measurements were performed on MgB(2) single crystals to determine the magnitude, symmetry, and temperature dependence of the superconducting gap. A single sharp peak due to Cooper pair breaking appears in the electronic continuum below T(c), reaching a maximum Raman shift of 105 +/- 1 cm(-1) [2 Delta(0)/k(B)T(c) = 3.96 +/- 0.09] and showing up to 5 cm(-1) anisotropy between polarized and depolarized spectra. The temperature dependence of 2 Delta follows that predicted from BCS theory, while the anisotropy decreases with decreasing temperature. It is concluded that the Raman results are consistent with a slightly anisotropic s-wave gap in a conventional BCS superconductor. PMID:11863969
Quilty, J W; Lee, S; Yamamoto, A; Tajima, S
Evidence for two separate energy gaps in underdoped high-temperature cuprate superconductors from broadband infrared ellipsometry.
We present broadband infrared ellipsometry measurements of the c-axis conductivity of underdoped RBa_{2}Cu_{3}O_{7-delta} (R=Y, Nd, and La) single crystals. Our data show that separate energy scales are underlying the redistributions of spectral weight due to the normal state pseudogap and the superconducting gap. Furthermore, they provide evidence that these gaps do not share the same electronic states and do not merge on the overdoped side. Accordingly, our data are suggestive of a two gap scenario with a pseudogap that is likely extrinsic with respect to superconductivity. PMID:18518326
Yu, Li; Munzar, D; Boris, A V; Yordanov, P; Chaloupka, J; Wolf, Th; Lin, C T; Keimer, B; Bernhard, C
Spatial inhomogeneity of the superconducting gap and order parameter in FeSe0.4Te0.6
We have performed a low-temperature scanning tunneling microscopy and spectroscopy study of the iron chalcogenide superconductor FeSe0.4Te0.6 with TC?14 K. Spatially resolved measurements of the superconducting gap reveal substantial inhomogeneity on a nanometer length scale. Analysis of the structure of the gap seen in tunneling spectra by comparison with calculated spectra for different superconducting order parameters (s-wave, d-wave, and anisotropic s-wave) yields the best agreement for an order parameter with anisotropic s-wave symmetry with an anisotropy of ś40%. The temperature dependence of the superconducting gap observed in places with large and small gap size indicates that it is indeed the superconducting transition temperature which is inhomogeneous. The temperature dependence of the gap size has been found to differ from the one predicted by BCS theory. An analysis of the local gap size in relation to the local chemical composition shows almost no correlation with the local concentration of Se/Te atoms at the surface.
Singh, U. R.; White, S. C.; Schmaus, S.; Tsurkan, V.; Loidl, A.; Deisenhofer, J.; Wahl, P.
Two energy scales and close relationship between the pseudogap and superconductivity in underdoped cuprate superconductors
By measuring the low temperature specific heat, the low energy quasi-particle excitation has been derived and analysed in systematically doped La 2- xSr xCuO 4 single crystals. The VolovikÆs relation predicted for a d-wave superconductor has been well demonstrated in wide doping regime, showing a robust evidence for the d-wave pairing symmetry. Furthermore the nodal gap slope v? of the superconducting gap is derived and is found to follow the same doping dependence of the pseudogap obtained from ARPES and tunnelling measurement. This strongly suggests a close relationship between the pseudogap and superconductivity. Taking the entropy conservation into account, we argue that the ground state of the pseudogap phase should have Fermi arcs with finite density of states at 0 K, and the transport data show that it behaves like an insulator due to probably weak localization. A nodal metal picture for the pseudogap phase cannot interpret the data. Based on the Fermi arc picture for the pseudogap phase it is found that the superconducting energy scale or Tc in underdoped regime is governed by both the maximum gap and the spectral weight from the Fermi arcs. This suggests that there are two energy scales: superconducting energy scale and the pseudogap. The superconductivity may be formed by the condensation of Fermi arc quasiparticles through pairing mediated by exchanging virtue bosons.
Wen, Hai-Hu; Wen, Xiao-Gang
Spontaneous Raman scattering and femtosecond time-resolved pump-probe spectroscopy are used to study and characterize material properties in superconductors, bulk semiconductors and semiconducting quantum dots. Superconducting gap oscillations are observed for the first time in MgB 2 (Tc = 39 K) and 2H-NbSe2 ( Tc = 7 K). In MgB2, multiple superconducting gap oscillations are observed at 24 cm-1, 103 cm -1 and ś44 cm-1. These frequencies are in reasonable agreement with other reported experimental results and published theoretical models. Spontaneous Raman measurements on MgB2 show a single strong resonance at 107 cm-1 near the superconducting gap. Consistent with spontaneous Raman measurement, coherent superconducting gap oscillations in 2H-NbSe2 are observed at 18 cm-1 (E symmetry) and 14 cm-1 ( A symmetry). The analysis suggests that a non-Raman mechanism or impurities are responsible for the observed oscillations in MgB2. Spontaneous Raman spectra of MgB2 show a large frequency shift in the optical E2g phonon from 580 cm-1 at 300 K to 630 cm-1 at 3 K due to anharmonicity. The resonance at the superconducting gap frequency shows a strong asymmetric lineshape near Tc, becoming Lorentzian-like near 3 K due to spectral weight gain at low frequencies. In ZnO, a study of the anharmonic properties of the low-frequency E2 optical phonon, using pump-probe spectroscopy, show an unusually long lifetime ś2 orders of magnitude larger for most optical modes in semiconductors. At 5 K, the frequency and lifetime are (2.9787 +/- 0.0002) THz and (211 +/- 7) ps. The temperature dependence of the lifetime is determined by up-conversion decay contributions, which vanish at zero temperature. The results show that the lifetime is limited by isotopic disorder and that nanosecond lifetimes may be achievable in isotopically-pure samples. In CdTe1-xSex quantum dots, two longitudinal optical phonons and a mixed mode are identified. The amplitude of the optical modes as a function of the laser wavelength agrees with the impulsive stimulated Raman scattering mechanism. At low power densities, the frequency of the optical phonons deviates from spontaneous Raman scattering behavior, which is attributed to impurity state trapping. Size-selective excitation effects for the acoustic phonons are more noticeable in time-domain studies. The difference between the time-domain and spontaneous Raman studies is not understood. Acoustic phonons are observed in CdSe quantum dots at 37 cm-1, 22 cm-1 and 5 cm-1 at 560 nm. The linewidth of the mode at 37 cm-1 shows a strong dependence on dot size and a linear dependence with temperature.
Aku-Leh, Cynthia
Doping dependence of the superconducting gap in Tl2Ba2CuO6+? from heat transport
We present low-temperature thermal conductivity measurements on the cuprate Tl2Ba2CuO6+? throughout the overdoped regime. In the T?0 limit, the thermal conductivity due to d -wave nodal quasiparticles provides a bulk measurement of the superconducting gap ? . We find ? to decrease with increasing doping, with a magnitude consistent with spectroscopic measurements (photoemission and tunneling). This argues for a pure and simple d -wave superconducting state in the overdoped region of the phase diagram, which appears to extend into the underdoped regime down to a hole concentration of ?0.1 hole/Cu. As hole concentration is decreased, the gap-to- Tc ratio increases, showing that the suppression of the superconducting transition temperature Tc (relative to the gap) begins in the overdoped regime.
Hawthorn, D. G.; Li, S. Y.; Sutherland, M.; Boaknin, Etienne; Hill, R. W.; Proust, C.; Ronning, F.; Tanatar, M. A.; Paglione, Johnpierre; Taillefer, Louis; Peets, D.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Kolesnikov, N. N.
Energy Evacuation from Cryostatically Nonstabilized Superconducting Magnets.
The investigation of the efficiency of energy evacuation and calculation of maximum temperature of the coil winding of a laboratory superconducting solenoid (0.15 kA; 8T; 50kJ) are presented. The coil winding made of internal stabilized conductor has no c...
N. G. Anishchenko R. Lyudemann G. P. Tsvineva Y. A. Shishov
On the organic energy gap problem
In conjugated organic molecules, the difference between the HOMO and LUMO Kohn-Sham eigenvalues is significantly smaller than the transport gap measured experimentally. We discuss here, within a local-orbital formulation of DFT, how this problem can be corrected using appropriate hybrid potentials, that add a fraction of Hartree-Fock exchange interaction in the DFT calculation. We illustrate this approach presenting calculations for two simple systems: H2 and C6H6; then, we discuss how to implement this hybrid approach in a general local-orbital calculation, adjusting the hybrid contribution to yield the correct experimental HOMO/LUMO energy gap for the molecule. We also consider the case of an organic molecule on a metal and analyze the effect of the molecule-metal interaction on the organic energy gap. In particular, we discuss how to introduce in this hybrid-potential scheme the effect of the image potential, and present results for the organic molecules PTCDA, TTF, benzene and pentacene on the metal surfaces Au(111), Ag(111) and Cu(111).
Flores, F.; Abad, E.; MartĒnez, J. I.; Pieczyrak, B.; Ortega, J.
Gap-Inhomogeneity-Induced Electronic States in Superconducting Bi2Sr2CaCu2O8+delta
In this Letter, we analyze, using scanning tunneling spectroscopy, the density of electronic states in nearly optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} in zero magnetic field. Focusing on the superconducting gap, we find patches of what appear to be two different phases in a background of some average gap, one with a relatively small gap and sharp large coherence peaks and one characterized by a large gap with broad weak coherence peaks. We compare these spectra with calculations of the local density of states for a simple phenomenological model in which a 2{zeta}{sub 0} x 2{zeta}{sub 0} patch with an enhanced or suppressed d-wave gap amplitude is embedded in a region with a uniform average d-wave gap.
Fang, A.C.
Evidence for two-gap superconductivity in the non-centrosymmetric compound LaNiC2
We study the superconducting properties of the non-centrosymmetric compound LaNiC2 by measuring the London penetration depth ??(T), the specific heat C(T,B) and the electrical resistivity ?(T,B). Both ??(T) and the electronic specific heat Ce(T) exhibit behavior at low temperatures that can be described in terms of a phenomenological two-gap Bardeen-Cooper-Schrieffer (BCS) model. The residual Sommerfeld coefficient in the superconducting state, ?0(B), shows a rapid increase at low fields and then an eventual saturation with increasing magnetic field. A pronounced upturn curvature is observed in the upper critical field Bc2(T) near Tc. All these experimental observations support the existence of two-gap superconductivity in LaNiC2.
Chen, J.; Jiao, L.; Zhang, J. L.; Chen, Y.; Yang, L.; Nicklas, M.; Steglich, F.; Yuan, H. Q.
Theory and Application of Superconducting Magnetic Energy Storage
Superconducting magnetic energy storage (SMES) technology is one of the most active research areas of applied superconductivity in the recent years especially after the high temperature superconducting (HTS) materials were discovered. The theory of SMES and the structure of its system will be introduced and discussed in this paper, as well as its power conditioning system control strategies and prospective
Ju Wen; Jian X. Jin; You G. Guo; Jian G. Zhu
NMR Study of Two-Gap Superconductivity in Lu2Fe3Si5
We report 175Lu and 29Si NMR results of the ternary-iron silicide superconductor, Lu2Fe3Si5, with Tcś 6.1 K. We confirm the decrease of the Knight shift and the existence of coherence peak of nuclear spin--lattice relaxation rate, 1/T1 of 29Si below Tc, indicating apparently that the superconducting (SC) pairing symmetry is of the spin-singlet. The observed 175Lu-NMR signals are attributed to the Zeeman split ?|▒ 1/2> transition under a large nuclear quadrupole interaction. The temperature dependence of 1/T1 of 175Lu obeys a Curie--Weiss behavior in the normal state. In the SC state, 1/T1 decreases rapidly, and follows the T1T=const. relation below T=1 K, which is suggestive of the existence of the residual density of states of the conduction electrons at the Fermi level. This indicates that the small SC gap is completely suppressed even at small field of H<1.3 T, and contributes to the residual Knight shift and 1/T1 in the SC state. We speculate that the small and large SC gap are associated with the electron-like (3D-Fermi surface) and the quasi-1D hole-like pocket bands, respectively.
Saeed, Muhammad; Wazumi, Toshihiro; Kumagai, Ken-ichi; Nakajima, Yasuyuki; Tamegai, Tsuyoshi
Ion-size effects in HTS cuprates - superfluid density and energy gaps
The demonstrated central role that ion size plays in determining Tc in the HTS cuprates needs to be further explored in order to determine whether the demonstrated systematic behaviour plays out in other superconducting properties. After all, Tc can be diminished simply by disorder effects. What is the effect of systematic ion-size variation on the superfluid density and superconducting energy gap? And can these effects be used to infer details concerning the pairing mechanism? To address these issues we report the effect of changing ion size on muon spin relaxation measurements of the superfluid density and Raman measurements of the superconducting gap in the model system RA2Cu3Oy (where R = La,..., Lu and A=Ba2-xSrx). The electronic density of states is determined from the effect of Zn substitution in this system and we are able to discount disorder scattering as the source of the systematic changes in superconducting properties. Our results confirm a picture where the polarizability of the charge-reservoir layer plays a key role in setting the energy scale for pairing in this system.
Mallett, Benjamin; Bernhard, Christian; Wolf, Thomas; Gilioli, Edi; Tallon, Jeff
Superconducting condensation energy of CeCu2Si2 and theoretical implications
Unconventional superconductivity occurs in a broad range of strongly correlated electron systems including the newly discovered iron pnictides and chalcogenides, various intermetallic rare earth metals, the cuprates and the organic superconductors. These systems are not only of varying effective dimensionality but their parent compounds out of which superconductivity emerges ranges from metals to bad metals and Mott insulators. The only unifying characteristic features seems that unconventional superconductivity occurs in close vicinity of zero-temperature instabilities which are most often magnetic in nature. Heavy fermion compounds represent prototype systems to address the interplay between quantum criticality and unconventional superconductivity [1]. In CeCu2Si2, the magnetic quantum phase transition and superconductivity occur at ambient pressure which allows for a detailed study of the energetics across the superconducting transition. Based on an in-depth study of the magnetic excitation spectrum of CeCu2Si2 in the normal and superconducting state we obtain a lower bound for the change in exchange energy [2]. The comparison with the superconducting condensation energy demonstrates that the built-up of magnetic correlations near the quantum critical point does drive superconductivity in CeCu2Si2. In addition, our comparison establishes a huge kinetic energy loss which we relate to the competition of Kondo screening and superconductivity as the opening of the gap weakens the Kondo effect [2,3]. We discuss the relation between kinetic energy loss and the nature of the underlying quantum critical point [1,3]. Our unexpected findings sheds further light on the emerging global phase diagram of heavy fermion compounds [4] and are believed to be relevant to other families of superconductivity which are also located in close proximity to magnetism.[4pt] [1] O. Stockert, S. Kirchner, F. Steglich, Q. Si, ``Superconductivity in Ce- and U-based 122 heavy-fermion compounds,'' to be published in JPSJ (invited review paper).[0pt] [2] O. Stockert, J. Arndt, E. Faulhaber, C. Geibel, H. S. Jeevan, S. Kirchner, M. Loewenhaupt, K. Schmalzl, W. Schmidt, Q. Si, F. Steglich, ``Magnetically driven superconductivity in CeCu2Si2,'' Nature Physics, 7, 119-124 (2011).[0pt] [3] S. Kirchner and Q. Si, to be published.[0pt] [4] Q. Si, ``Quantum Criticality and Global Phase Diagram of Magnetic Heavy Fermions,'' Phys. Status Solidi B247, 476 (2010).
Kirchner, Stefan
Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212
The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high- T c cuprate, Bi2Sr2CaCu2 O8+ ? (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening.
Ino, Akihiro; Anzai, Hiroaki; Arita, Masashi; Namatame, Hirofumi; Taniguchi, Masaki; Ishikado, Motoyuki; Fujita, Kazuhiro; Ishida, Shigeyuki; Uchida, Shinichi
The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-Tc cuprate, Bi2Sr2CaCu2 O8+? (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening.
Determination of the electron-phonon coupling constants from the experimental temperature dependences of superconducting gaps in MgB2
Experimental temperature dependences ??, ?( T) of the energy of superconducting gaps for MgB2 samples with the critical temperatures 22 K < T c < 41 K have been fitted by selecting the renormalized electron-phonon coupling constants ? ij with the use of the Moskalenko-Shul system of equations, the expression for the frequency of collective plasma oscillations obtained by Leggett for two-gap superconductors, and two fitting parameters. We previously obtained the dependences ??, ?( T) by the multiple Andreev reflection spectroscopy of superconductor-constriction-superconductor junctions based on MgB2 with various degree of disorder of the crystal structure. It has been shown that the intraband pairing constants are decisive for the superconductivity mechanism in MgB2; in this case, ? V ?? V ??/ V ?? = 8-22 and the ratio of the interband constants ? can range from 3 to 11. The set of the Eliashberg coupling constants ? {/ij 0} has been qualitatively determined for relatively pure MgB2 with maximum values T c ? 40 K. The leading constant is 0.7 < ?{??/0} ? ?{eff/0} < 0.9 and depends on the choice of the upper integration limit in the Bardeen-Cooper-Schrieffer (BCS) model and the effective Coulomb repulsion ?{iff/*}. The characteristic ratio for the gap in the ? band is 2??/ k B T c = 5.0-6.5.
Kuzmichev, S. A.; Kuzmicheva, T. E.; Tchesnokov, S. N.
Total energy intake, adolescent discretionary behaviors and the energy gap
Objective:To estimate total energy intake and the energy gapŚthe daily imbalance between energy intake and expenditureŚassociated with discretionary behaviors of adolescents, namely their leisure active behaviors (playing or participating in sports and heavy chores), leisure sedentary behaviors (television (TV) viewing and playing video and computer games), productive sedentary behaviors (reading or doing homework).Design:Prospective observational study.Participants:A total of 538 students (mean
K R Sonneville; S L Gortmaker
Research for superconducting energy storage patterns and its practical countermeasures
In this paper, we attempt to introduce briefly the significance, the present status, as well as the working principle of the primary patterns of the superconducting energy storage system, first of all. According to the defect on the lower energy storage density of existed superconducting energy storage device, we proposed some new ideas and strategies about how to improve the energy storage density, in which, a brand-new but a tentative proposal regarding the concept of energy compression was emphasized. This investigation has a certain reference value towards the practical application of the superconducting energy storage.
Lin, D. H.; Cui, D. J.; Li, B.; Teng, Y.; Zheng, G. L.; Wang, X. Q.
To Close or Not to Close: The Fate of the Superconducting Gap Across the Topological Quantum Phase Transition in Majorana-Carrying Semiconductor Nanowires
We investigate theoretically the low-energy physics of semiconductor Majorana wires in the vicinity of a magnetic field-driven topological quantum phase transition (TQPT). The local density of states at the end of the wire, which is directly related to the differential conductance in the limit of point-contact tunneling, is calculated numerically. We find that the dependence of the end-of-wire local density of states on the magnetic field is nonuniversal and that the signatures associated with the closing of the superconducting gap at the Majorana TQPT are essentially invisible within a significant range of experimentally relevant parameters. Our results provide a possible explanation for the recent observation of the apparent nonclosure of the gap at the Majorana TQPT in semiconductor nanowires.
Stanescu, Tudor D.; Tewari, Sumanta; Sau, Jay D.; Das Sarma, S.
Tunneling study of superconductivity near the metal-insulator transition
By electron tunneling we have studied the superconducting properties of granular aluminum as one approaches the metal-insulator transition. We find that with increasing sample resistivity, the superconducting energy-gap edge broadens because of lifetime effects until that broadening becomes comparable to the gap. At this point, superconductivity disappears.
R. C. Dynes; J. P. Garno; G. B. Hertel; T. P. Orlando
Dynes, R.C.; Garno, J.P.; Hertel, G.B.; Orlando, T.P.
Superconducting Magnetic Energy Storage for Electric Utilities and Fusion Systems.
Superconducting inductors provide a compact and efficient means of storing electrical energy without an intermediate conversion process. Energy storage inductors are under development for load leveling and transmission line stabilization in electric utili...
J. D. Rogers, H. J. Boenig, W. V. Hassenzahl
Anisotropic Superconducting Gap Revealed by Angle Resolved Specific Heat, Point Contact Tunneling and Scanning Tunneling Microscope in Iron Pnictide Superconductors
Angle resolved specific heat was measured in FeSe0.55Te0.45 single crystals. A four-fold oscillation of C/T, with the minimum locating at the Fe-Fe bond direction, was observed when the sample was rotated at 9 T, which can be understood as due to the gap modulation on the electron pocket within the scheme of S▒ pairing. Accordingly, by measuring the point contact Andreev reflection spectrum on the BaFe2-xNixAs2 single crystals in wide doping regimes, we found a crossover from nodeless to nodal feature of the superconducting gap. In K-doped BaFe2As2 single crystals, we performed the low temperature STM measurements and observed a well ordered vortex lattice in local region. In addition, the statistics on over 3000 dI/dV spectra illustrate clear evidence of two gaps with magnitude of 7.6 meV and 3.3 meV, respectively. Detailed fitting to the tunneling spectrum shows an isotropic superconducting gap. Work collaborated with B. Zeng, C. Ren, L. Shan, Y. L. Wang, B. Shen, G. Mu, H. Q. Luo, T. Xiang, H. Yang, I. I. Mazin and P. C. Dai. References: [4pt] [1] B. Zeng, et al., arXiv:1007.3597, Nature Communications, 2010, in press.[0pt] [2] C. Ren, et al., to be published.[0pt] [3] L. Shan, et al., arXiv:1005.4038.
Wen, Hai-Hu
Method for making mirrored surfaces comprising superconducting material
Superconducting mirror surfaces are provided by forming a mirror surface from a material which is superconductive at a temperature above about 40.degree. K. and adjusting the temperature of the surface to that temperature at which the material is superconducting. The mirror surfaces are essentially perfect reflectors for electromagnetic radiation with photon energy less than the superconducting band gap.
Early, James T. (Livermore, CA); Hargrove, R. Steven (Danville, CA)
Flywheel energy storage using superconducting magnetic bearings
Storage of electrical energy on a utility scale is currently not practicable for most utilities, preventing the full utilization of existing base-load capacity. A potential solution to this problem is Flywheel Energy Storage (FES), made possible by technological developments in high-temperature superconducting materials. Commonwealth Research Corporation (CRC), the research arm of Commonwealth Edison Company, and Argonne National Laboratory are implementing a demonstration project to advance the state of the art in high temperature superconductor (HTS) bearing performance and the overall demonstration of efficient Flywheel Energy Storage. Currently, electricity must be used simultaneously with its generation as electrical energy storage is not available for most utilities. Existing storage methods either are dependent on special geography, are too expensive, or are too inefficient. Without energy storage, electric utilities, such as Commonwealth Edison Company, are forced to cycle base load power plants to meet load swings in hourly customer demand. Demand can change by as much as 30% over a 12-hour period and result in significant costs to utilities as power plant output is adjusted to meet these changes. HTS FES systems can reduce demand-based power plant cycling by storing unused nighttime capacity until it is needed to meet daytime demand.
Abboud, R. G.; Uherka, K.; Hull, J.; Mulcahy, T.
Superconducting magnetic energy storage for asynchronous electrical systems
A superconducting magnetic energy storage coil connected in parallel between converters of two or more ac power systems provides load leveling and stability improvement to any or all of the ac systems. Control is provided to direct the charging and independently the discharging of the superconducting coil to at least a selected one of the ac power systems.
Boenig, Heinrich J. (Los Alamos, NM)
Effects of Fermi surface and superconducting gap structure in field-rotational experiments: A possible explanation for the cusplike singularity in Y Ni2 B2 C
We have studied the field-orientational dependence of the zero-energy density of states (FODOS) for a series of systems with different Fermi surface and superconducting gap structures. Instead of the phenomenological Doppler-shift method, we use an approximate analytical solution of the Eilenberger equation together with self-consistent determination of the order parameter and a variational treatment of the vortex lattice. First, we compare the zero-energy density of states when a magnetic field is applied in the nodal direction [?node(0)] and in the antinodal direction [?anti(0)] , by taking account of the field-angle dependence of the order parameter. As a result, we found that there exists a crossover magnetic field H* so that ?anti(0)>?node(0) for H?anti(0) for H>H* , consistent with our previous analyses. Next, we showed that H* and the shape of the FODOS are determined by a contribution from the small part of the Fermi surface where the Fermi velocity is parallel to the field-rotational plane. In particular, we found that H* is lowered and the FODOS has broader minima when a superconducting gap has point nodes, in contrast to the result of the Doppler-shift method. We also studied the effects of in-plane anisotropy of the Fermi surface. We found that the in-plane anisotropy of a quasi-two-dimensional Fermi surface sometimes becomes larger than the effects of the Doppler shift and can destroy the Doppler-shift-predominant region. In particular, this tendency is strong in a multiband system where superconducting coherence lengths are isotropic. Finally, we addressed the problem of the cusplike singularity in YNi2B2C and present a possible explanation of this phenomenon.
Orbital-selective superconductivity, gap anisotropy, and spin resonance excitations in a multiorbital t-J1-J2 model for iron pnictides
We study the orbital-selective superconducting pairing in a five-orbital t-J1-J2 model for iron pnictides. Depending on the orbital selectivity of electron correlations and the orbital characters along the Fermi surface, the superconducting gap in an A1g pairing state may exhibit anisotropy. This anisotropy varies with the degree of J1-J2 magnetic frustration. In the superconducting state, the frequency dependence of the dynamical spin susceptibility at the antiferromagnetic wave vector (?,0) shows a resonance, whose width is enhanced by the orbital selectivity of the superconducting gap. When the degree of the orbital selectivity is sufficiently strong, the resonance peak may be split in two. We discuss the implications of our results on the recent angle-resolved photoemission and neutron-scattering measurements in several superconducting iron pnictides.
Yu, Rong; Zhu, Jian-Xin; Si, Qimiao
Optimizing the configuration of a superconducting photonic band gap accelerator cavity to increase the maximum achievable gradients
We present a design of a superconducting rf photonic band gap (SRF PBG) accelerator cell with specially shaped rods in order to reduce peak surface magnetic fields and improve the effectiveness of the PBG structure for suppression of higher order modes (HOMs). The ability of PBG structures to suppress long-range wakefields is especially beneficial for superconducting electron accelerators for high power free-electron lasers (FELs), which are designed to provide high current continuous duty electron beams. Using PBG structures to reduce the prominent beam-breakup phenomena due to HOMs will allow significantly increased beam-breakup thresholds. As a result, there will be possibilities for increasing the operation frequency of SRF accelerators and for the development of novel compact high-current accelerator modules for the FELs.
Simakov, Evgenya I.; Kurennoy, Sergey S.; O'Hara, James F.; Olivas, Eric R.; Shchegolkov, Dmitry Yu.
This book explains the theoretical background of superconductivity. Includes discussion of electricity, material fabrication, maglev trains, the superconducting supercollider, and Japanese-US competition. The authors reports the latest discoveries.
Langone, J.
Superconducting magnetic energy storage for power system transient stability improvement.
This paper shows, through a feasibility study carried out with the Hydro-Quebec ST-600 transient stability program, how a SMES (Superconducting Magnetic Energy Storage) can improve the transient stability and the damping of power systems either by active ...
P. Nonnon M. Gavrilovic G. Begin
Electric utility benefits of superconducting magnetic energy storage.
This paper summarizes a preliminary scoping analysis to illustrate examples of the benefits electric utilities might derive from Superconducting Magnetic Energy Storage (SMES). A major objective of the study was to show that, even though SMES technology i...
J. G. De Steese J. E. Dagle
BCS superconductivity in metallic nanograins: Finite-size corrections, low-energy excitations, and robustness of shell effects
We combine the BCS self-consistency condition, a semiclassical expansion for the spectral density and interaction matrix elements to describe analytically how the superconducting gap depends on the size and shape of a two- and three-dimensional superconducting grain. In chaotic grains mesoscopic fluctuations of the matrix elements lead to a smooth dependence of the order parameter on the excitation energy. In the integrable case we find shell effects; i.e., for certain values of the electron number N a small change in N leads to large changes in the energy gap. With regard to possible experimental tests we provide a detailed analysis of the dependence of the gap on the coherence length and the robustness of shell effects under small geometrical deformations.
GarcĒa-GarcĒa, Antonio M.; Urbina, Juan Diego; Yuzbashyan, Emil A.; Richter, Klaus; Altshuler, Boris L.
Peculiarities of the superconducting gaps and the electron-boson interaction in TmNi2B2C as seen by point-contact spectroscopy
Point-contact (PC) investigations on the title compound in the normal and superconducting (SC) state (Tc?10.6 K) are presented. The temperature dependence of the SC gap of TmNi2B2C determined from Andreev-reflection (AR) spectra using the standard single-gap approximation (SGA) deviates from the BCS behavior in displaying a maximum at about Tc/2. A refined analysis within the two-gap approximation provides evidence for the presence of a second gap twice as large as the main gap (the first one), while the latter is close to that within the SGA. This way, TmNi2B2C expands the number of nickel borocarbide superconductors which exhibit a clear multiband character. Additionally, ōreentrantö features were found in the AR spectra for some PCs measured in a magnetic field. The PC spectroscopy of the electron-boson interaction in TmNi2B2C in the normal state reveals a pronounced phonon maximum at 9.5 meV and a more smeared one at around 15 meV, while at higher energies the PC spectra are almost featureless. Additionally, the most intense peak slightly above 3 meV observed in the PC spectra of TmNi2B2C is presumably caused by crystalline-electric-field (CEF) excitations. The peak near 1 meV detected for some PC spectra is connected with a modification of the CEF, probably due to boron or carbon vacancies, allowing a probe of the local stoichiometry by PC spectroscopy.
Naidyuk, Yu. G.; Kvitnitskaya, O. E.; Tiutrina, L. V.; Yanson, I. K.; Behr, G.; Fuchs, G.; Drechsler, S.-L.; Nenkov, K.; Schultz, L.
Toroidal constant-tension superconducting magnetic energy storage units
A superconducting magnetic energy storage unit is provided in which the magnet is wound in a toroidal fashion such that the magnetic field produced is contained only within the bore of the magnet, and thus producing a very low external field. The superconducting magnet includes a coolant channel disposed through the wire. The bore of the magnet comprises a storage volume in which cryogenic coolant is stored, and this volume supplies the coolant to be delivered to the coolant channel in the magnet.
Herring, J. Stephen (Idaho Falls, ID)
Probing the superconducting gap of UPt 3 by very low-temperature thermal conductivity
We present new measurements of the thermal conductivity of UPt 3 at very low temperature( T ? 16 mK) and under magnetic field. We discuss in detail how our measurements (in zero field anfinite fields) may help to determine the symmetry of the superconducting order parameter.
Suderow, H.; Brison, J. P.; Huxley, A. D.; Flouquet, J.
Is There an Energy Efficiency Gap?
Many analysts have argued that energy efficiency investments offer an enormous ōwin-winö opportunity to both reduce negative externalities and save money. This overview paper presents a simple model of investment in energy-using capital stock with two types of market failures: first, uninternalized externalities from energy consumption, and second, forces such as imperfect information that cause consumers and firms not to
Hunt Allcott; Michael Greenstone
Superconducting magnetic bearing for a flywheel energy storage system using superconducting coils and bulk superconductors
Stable levitation or suspension of a heavy object in mid-air can be realized using a combination of a permanent magnet and a bulk superconductor with high critical current density, in that the force density has reached 100 kN/m 2. The superconducting flywheel system for energy storage is attractive due to a great reduction in the rotational loss of the bearings. So long as a permanent magnet is used as a magnetic source, however, the electromagnetic force (EMF) is essentially limited by its field strength. In order to overcome such a limitation, we employed a superconducting coil/magnet as a magnetic source and studied the EMF characteristics of bulk superconductors in high-magnetic fields. We also measured the EMF between a bulk superconductor and a specially designed superconducting coil having a high field gradient, and confirmed that the EMF reached 9450 N (force density: 2507 kN/m 2).
Nagashima, K.; Seino, H.; Sakai, N.; Murakami, M.
Orbital-selective metal-insulator transition and gap formation above TC in superconducting Rb(1-x)Fe(2-y)Se2.
Understanding the origin of high-temperature superconductivity in copper- and iron-based materials is one of the outstanding tasks of current research in condensed matter physics. Even the normal metallic state of these materials exhibits unusual properties. Here we report on a hierarchy of temperatures T(c)gap)superconducting Rb(1-x)Fe(2-y)Se(2) observed by THz spectroscopy (T(c)=critical temperature of the superconducting phase; T(gap)=temperature below which an excitation gap opens; T(met)=temperature below which a metallic optical response occurs). Above T(met)=90 K the material reveals semiconducting characteristics. Below T(met) a coherent metallic THz response emerges. This metal-to-insulator-type, orbital-selective transition is indicated by an isosbestic point in the temperature dependence of the optical conductivity and dielectric constant at THz frequencies. At T(gap)= 61 K, a gap opens in the THz regime and then the superconducting transition occurs at T(c)=32 K. This sequence of temperatures seems to reflect a corresponding hierarchy of the electronic correlations in different bands. PMID:24469424
Wang, Zhe; Schmidt, M; Fischer, J; Tsurkan, V; Greger, M; Vollhardt, D; Loidl, A; Deisenhofer, J
Quasiparticle Energies and Band Gaps in Graphene Nanoribbons
We present calculations of the quasiparticle energies and band gaps of graphene nanoribbons (GNRs) carried out using a first-principles many-electron Green's function approach within the GW approximation. Because of the quasi-one-dimensional nature of a GNR, electron-electron interaction effects due to the enhanced screened Coulomb interaction and confinement geometry greatly influence the quasiparticle band gap. Compared with previous tight-binding and density
Li Yang; Cheol-Hwan Park; Young-Woo Son; Marvin L. Cohen; Steven G. Louie
Energy BandGap Engineering of Graphene Nanoribbons
We investigate electronic transport in lithographically patterned graphene\\u000aribbon structures where the lateral confinement of charge carriers creates an\\u000aenergy gap near the charge neutrality point. Individual graphene layers are\\u000acontacted with metal electrodes and patterned into ribbons of varying widths\\u000aand different crystallographic orientations. The temperature dependent\\u000aconductance measurements show larger energy gaps opening for narrower ribbons.\\u000aThe sizes
Melinda Y. Han; Barbaros Ozyilmaz; Yuanbo Zhang; Philip Kim
Evidence for excluding the possibility of d-wave superconducting-gap symmetry in Ba-doped KFe2As2
We have investigated the superconducting (SC)-gap anisotropy for several Ba-doped KFe2As2 samples using laser-based angle-resolved photoemission spectroscopy. We show that the SC-gap anisotropy and node positions drastically change with a small amount of Ba doping. Our results totally exclude a possibility of d-wave symmetry and strongly suggest that both spin and orbital fluctuations are important for the pairing interaction in the Ba-doped K122.
Ota, Y.; Okazaki, K.; Kotani, Y.; Shimojima, T.; Malaeb, W.; Watanabe, S.; Chen, C.-T.; Kihou, K.; Lee, C. H.; Iyo, A.; Eisaki, H.; Saito, T.; Fukazawa, H.; Kohori, Y.; Shin, S.
Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212.
: The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-Tc cuprate, Bi2Sr2CaCu2 O8+? (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening. PMID:24314035
Thermal conductivity and gap structure of the superconducting phases of UPt3
We present new measurements of the thermal conductivity of UPt3 down to very low temperatures (16mK) and under magnetic fields (up to 4 T) which cover all the superconducting phases of UPt3. The measurements in zero field are compared with recent theoretical predictions for the thermal conductivity, which is dominated by impurity states at the lowest temperatures studied. The measurements under magnetic field at low temperatures are surprising since they don't show the expected low field square root dependence. The discontinuity of d kappa/dT at Tc changes drastically when passing from the high field low temperature C phase to the low field high temperature A phase : this is related to the change of the symmetry of the superconducting order parameter when crossing the A - C phase transition.
Suderow, H.; Brison, J. P.; Huxley, A.; Flouquet, J.
Thermal conductivity and gap structure of the superconducting phases of UPt{sub 3}
We present new measurements of the thermal conductivity ({kappa}) of Upt{sub 3} down to very low temperatures (16 mK) and under magnetic fields (up to 4 T) which cover all the superconducting phases of Upt{sub 3}. The measurements in zero field are compared with recent theoretical predictions for the thermal conductivity, which is dominated by impurity states at the lowest temperatures studied. The measurements under magnetic field at low temperatures are surprising since they don`t show the expected low field square root dependence, {kappa} {proportional_to} {radical}B. The discontinuity of d{kappa}/dT at T{sub c} changes drastically when passing from the high field low temperature C phase to the low field high temperature A phase: this is related to the change of the symmetry of the superconducting order parameter when crossing the A {yields} C phase transition.
Suderow, H.; Huxley, A.; Flouquet, J. [CEA, Grenoble (France); Brison, J.P. [CNRS, Grenoble (France)
Energy gaps in "metallic" single-walled carbon nanotubes.
Metallic single-walled carbon nanotubes have been proposed to be good one-dimensional conductors. However, the finite curvature of the graphene sheet that forms the nanotubes and the broken symmetry due to the local environment may modify their electronic properties. We used low-temperature atomically resolved scanning tunneling microscopy to investigate zigzag and armchair nanotubes, both thought to be metallic. "Metallic" zigzag nanotubes were found to have energy gaps with magnitudes that depend inversely on the square of the tube radius, whereas isolated armchair tubes do not have energy gaps. Additionally, armchair nanotubes packed in bundles have pseudogaps, which exhibit an inverse dependence on tube radius. These observed energy gaps suggest that most "metallic" single-walled nanotubes are not true metals, and they have implications for our understanding of the electronic properties and potential applications of carbon nanotubes. PMID:11326093
Ouyang, M; Huang, J L; Cheung, C L; Lieber, C M
The author presents treatment of the field of superconductivity, from its inception in 1911 to the present day. Its discussions range from scientific aspects to applications in business, medicine, etc. This book provides definitions and a selective bibliography.
Mayo, J.L.
Spin-polaron theory of high-{Tc} superconductivity: 3, Gap function and critical temperature
Results from previous papers in this series are used to derive approximate expressions for the gap and {Tc} within the framework of a Cooper-pairing approach. The possible symmetry types of the gap are discussed. It is shown how the proximity of the Fermi level to the Mott-Hubbard band edge and the interplay of O 2p{sigma} and 2p{pi} bands and/or localization effects can provide good fits to the variation of {Tc} with x in La{sub 2-x}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 7-x}. It is concluded that the in-plane gap is either s- or d-like but anisotropic in either case. Other aspects and implications of the model and of the calculations are given and comparisons with Mott`s spin-bipolaron model are made.
Wood, R.F.
Energy Gaps in Etched Graphene Nanoribbons
Transport measurements on an etched graphene nanoribbon are presented. It is shown that two distinct voltage scales can be experimentally extracted that characterize the parameter region of suppressed conductance at low charge density in the ribbon. One of them is related to the charging energy of localized states, the other to the strength of the disorder potential. The lever arms
C. Stampfer; J. G³ttinger; S. Hellm³ller; F. Molitor; K. Ensslin; T. Ihn
The role of gap analyses in energy assurance planning.
Energy-related emergencies, such as power outages or interruptions to other energy supplies, can arise from a number of factors. Common causes include severe weather events--such as snowstorms, hurricanes, or summer storms with strong winds--as well as energy infrastructure that is overburdened, aging, or in need of repair. As past experience indicates, jurisdictions will continue to experience severe weather events, as well as confront infrastructure issues that make future power outages likely. As a result, state and local governments have turned to energy assurance planning, an energy-specific form of planning that helps jurisdictions prepare for and recover from energy emergencies. Energy assurance recognizes that power loss/disruption cannot be eradicated completely, but jurisdictions can mitigate the impact of power loss through effective planning. This article discusses the role of energy assurance planning and provides a description of what energy assurance means and why developing such plans at the state and local levels is important. In addition, this article discusses the role of statutory gap analyses in energy assurance planning and discusses how a gap analysis can be used by planners to identify trends and gaps in energy assurance. To provide context, a recently conducted statutory gap analysis analyzing national emergency backup power trends is provided as a case study. A summary of this project and key findings is included. Finally, this article briefly touches on legislation as an alternative to energy assurance planning, and provides summaries of recent legislative proposals introduced in the aftermath of Hurricane Sandy. PMID:24180061
Shea, Katherine
Doping-dependent anisotropic superconducting gap in Na1-?(Fe1-xCox)As from London penetration depth
The London penetration depth was measured in single crystals of self-doped Na1-?FeAs (from under doping to optimal doping, Tc from 14 to 27 K) and electron-doped Na(Fe1-xCox)As with x ranging from undoped, x=0, to overdoped, x=0.1. In all samples, the low-temperature variation of the penetration depth exhibits a power-law dependence, ??(T)=ATn, with the exponent that varies in a domelike fashion from nś1.1 in the underdoped, reaching a maximum of nś1.9 in the optimally doped, and decreasing again to nś1.3 on the overdoped side. While the anisotropy of the gap structure follows a universal domelike evolution, the exponent at optimal doping, nś1.9, is lower than in other charge-doped Fe-based superconductors (FeSCs). The full-temperature range superfluid density, ?s(T)=?(0)/?(T)2, at optimal doping is also distinctly different from other charge-doped FeSCs but is similar to isovalently substituted BaFe2(As1-xPx)2, believed to be a nodal pnictide at optimal doping. These results suggest that the superconducting gap in Na(Fe1-xCox)As is highly anisotropic even at optimal doping.
Cho, K.; Tanatar, M. A.; Spyrison, N.; Kim, H.; Song, Y.; Dai, Pengcheng; Zhang, C. L.; Prozorov, R.
Cho, Kyuil; Tanatar, Makariy A.; Spyrison, Nicholas; Kim, Hyunsoo; Song, Y.; Dai, Pengcheng; Zhang, C.L.; Prozorov, Ruslan
Impact of superconductive magnetic energy storage on electric power transmission
The authors demonstrate that a superconductive magnetic energy storage (SMES) system can provide a significant positive impact on electric power transmission. By using SMES, transmission-line loadings during heavy load hours can be reduced if the SMES system is located near the major load. Transmission losses as well as the fuel cost for the losses over a 24 hr period can
K.-S. Tam; P. Kumar
Control Aspects of the Tacoma Superconducting Magnetic Energy Storage Project
On February 16, 1983, a 10 MW\\/30 MJ superconducting magnetic energy storage unit was energized at the Bonneville Power Administration (BPA) substation in Tacoma, Washington. The unit was retired a year later, after extensive tests directed toward its experimental use as a small-signal stabilizer for the Pacific AC Intertie. This paper addresses the control aspects of the project. These include
J. F. Hauer; H. J. Boenig
A prototype of a flywheel system with auto stable high temperature superconducting bearings was built and tested. The bearings offered good vertical and lateral stability. A metallic flywheel disk, ° 190 mm x 30 mm, was safely rotated at speeds up to 15000 rpm. The disk was driven by a 3 phase synchronous homopolar motor\\/generator. Maximum energy capacity was 3.8
H. J. Bornemann; C. Urban; P. Boegler; T. Ritter; O. Zaitsev; K. Weber; H. Rietschel
Design of Superconducting High Energy Beam Line Dipole-Magnetostatics
Three relatively distinct designs of superconducting beam line dipoles have evolved at Fermilab. Two follow from Energy Doubler\\/ Saver considerations and one from POPAE considerations. Suitable end arrangements are placed on each coil to eliminate the field rise in the end conductors. An adjustment of the conductor locations within the body of the magnet then permits the elimination of sextupole
S. C. Snowdon
Evaluation of Superconducting Magnetic Energy Storage Systems. Final Report.
The study objective was to estimate the breakeven capital cost of Superconducting Magnetic Energy Storage (SMES) and its highest possible value. The results will be compared by EPRI to the capital cost of SMES being estimated by Bechtel in a related study...
S. T. Lee R. S. Albert D. T. Imamura
Low cost composite structures for superconducting magnetic energy storage systems
As part of the Superconducting Magnetic Energy Storage\\/Engineering Test Model (SMES-ETM) program, design, analysis, fabrication and test programs were conducted to evaluate the low cost manufacturing of fiberglass reinforced plastic (FRP) beams for usage as major components of the structural and electrical insulation systems. These studies utilized pultrusion process technologies and vinylester resins to produce large net sections at costs
Craig Rix; David McColskey; Robert Acree
A superconducting magnetic energy storage unit is provided in which the magnet is wound in a toroidal fashion such that the magnetic field produced is contained only within the bore of the magnet, and thus producing a very low external field. The superconducting magnet includes a coolant channel disposed through the wire. The bore of the magnet comprises a storage volume in which cryogenic coolant is stored, and this volume supplies the coolant to be delivered to the coolant channel in the magnet. 6 figs.
Herring, J.S.
Stripes and superconductivity in cuprate superconductors
One type of order that has been observed to compete with superconductivity in cuprates involves alternating charge and antiferromagnetic stripes. Recent neutron scattering studies indicate that the magnetic excitation spectrum of a stripe-ordered sample is very similar to that observed in superconducting samples. In fact, it now appears that there may be a universal magnetic spectrum for the cuprates. One likely implication of this universal spectrum is that stripes of a dynamic form are present in the superconducting samples. On cooling through the superconducting transition temperature, a gap opens in the magnetic spectrum, and the weight lost at low energy piles up above the gap; the transition temperature is correlated with the size of the spin gap. Depending on the magnitude of the spin gap with respect to the magnetic spectrum, the enhanced magnetic scattering at low temperature can be either commensurate or incommensurate. Connections between stripe correlations and superconductivity are discussed.
Tranquada, J. M.
Energy gaps in Bi(2)Sr(2)CaCu(2)O(8+?) cuprate superconductors.
The relationship between the cuprate pseudogap (?(p)) and superconducting gap (?(s)) remains an unsolved mystery. Here, we present a temperature- and doping-dependent tunneling study of submicron Bi(2)Sr(2)CaCu(2)O(8+?) intrinsic Josephson junctions, which provides a clear evidence that ?(s) closes at a temperature T(c) (0) well above the superconducting transition temperature T(c) but far below the pseudogap opening temperature T*. We show that the superconducting pairing first occurs predominantly on a limited Fermi surface near the node below T(c) (0), accompanied by a Fermi arc due to the lifetime effects of quasiparticles and Cooper pairs. The arc length has a linear temperature dependence, and as temperature decreases below T(c) it reduces to zero while pairing spreads to the antinodal region of the pseudogap leading to a d-wave superconducting gap on the entire Fermi surface at lower temperatures. PMID:22355760
Ren, J K; Zhu, X B; Yu, H F; Tian, Ye; Yang, H F; Gu, C Z; Wang, N L; Ren, Y F; Zhao, S P
Energy gaps in Bi2Sr2CaCu2O8+? cuprate superconductors
The relationship between the cuprate pseudogap (?p) and superconducting gap (?s) remains an unsolved mystery. Here, we present a temperature- and doping-dependent tunneling study of submicron Bi2Sr2CaCu2O8+? intrinsic Josephson junctions, which provides a clear evidence that ?s closes at a temperature Tc0 well above the superconducting transition temperature Tc but far below the pseudogap opening temperature T*. We show that the superconducting pairing first occurs predominantly on a limited Fermi surface near the node below Tc0, accompanied by a Fermi arc due to the lifetime effects of quasiparticles and Cooper pairs. The arc length has a linear temperature dependence, and as temperature decreases below Tc it reduces to zero while pairing spreads to the antinodal region of the pseudogap leading to a d-wave superconducting gap on the entire Fermi surface at lower temperatures.
Ren, J. K.; Zhu, X. B.; Yu, H. F.; Tian, Ye; Yang, H. F.; Gu, C. Z.; Wang, N. L.; Ren, Y. F.; Zhao, S. P.
In this paper a short historical account of the discovery of superconductivity and of its gradual development is given. The physical interpretation of its various aspects took about forty years (from 1911 to 1957) to reach a successful description of this phenomenon in terms of a microscopic theory At the very end it seemed that more or less everything could be reasonably interpreted even if modifications and refinements of the original theory were necessary. In 1986 the situation changed abruptly when a cautious but revolutionary paper appeared showing that superconductivity was found in certain ceramic oxides at temperatures above those up to then known. A rush of frantic experimental activity started world-wide and in less than one year it was shown that superconductivity is a much more widespread phenomenon than deemed before and can be found at temperatures well above the liquid air boiling point. The complexity and the number of the substances (mainly ceramic oxides) involved call for a sort of modern alchemy if compounds with the best superconducting properties are to be manufactured. We don't use the word alchemy in a deprecatory sense but just to emphasise that till now nobody can say why these compounds are what they are: superconductors.
Sacchetti, N.
Availability analysis of a 100 kWh superconducting magnetic energy storage.
Superconducting Magnetic Energy Storage (SMES) is one of the possible and useful applications of the modern superconducting technology. It is known that some loads on electricity distribution networks are particularly sensitive to short power interruption...
H. Maekinen R. Mikkonen
Quasiparticle Gaps and Exciton Coulomb Energies in Si Nanoshells
Quasiparticle gaps and exciton Coulomb energies of H-passivated spherical Si nanoshells are computed using rst principles SCF and GW methods. We nd that the quasiparticle gap of a nanoshell depends on both its inner radius R1 (weakly) and outer radius R2 (strongly). These dependences on R1 and R2 are mostly consistent with electrostatics of a metallic shell. We also nd that the unscreened Coulomb energy ECoul in Si nanoshells has a somewhat unexpected size dependence at xed outer radius R2: ECoul decreases as the nanoshell becomes more conning, contrary to what one would expect from quantum connement eects. We show that this is a consequence of an increase in the average electron-hole distance, giving rise to reduced exciton Coulomb energies in spite of the reduction in the conning nanoshell volume.
Frey, K. [University of Illinois, Chicago; Idrobo Tapia, Juan C [ORNL; Tiago, Murilo L [ORNL; Reboredo, Fernando A [ORNL; Ogut, Serdar [University of Illinois, Chicago
Superconducting energy storage development for electric utility systems
High load factors are desirable goals for all electric utilities to reduce the total power generation cost. Superconducting Magnetic Energy Storage (SMES) technology has progressed to the point where it shows promise as an alternate energy-storage method to pumped hydrostorage for improving electric-utility load factors. Experiments indicate that a SMES system responds quickly (i.e., in milliseconds) to power-system demand and
R. D. Turner; H. J. Boenig; W. V. Hassenzahl
Investigation of high-temperature superconducting flywheel energy storage devices
The paper studies a possibility of the technology of a high-temperature superconducting flywheel energy storage system and extracts its technical subjects. As a result of investigating the present status of technology and development of the flywheel for the electric energy storage system, it is found that it is a promising technology which has basically a wide applicability to multipurposes. A combination of the technology only with the existing element technology is fully feasible, and the system shows excellent performance in energy storage for medium-scale capacity for a relatively short period. However, there have been seen few application examples. For application to power systems and industrial systems, it is necessary to reduce operational loss of the system and to realize flywheels which can store much larger capacities of energy. It is proposed that a combination of high-temperature superconducting bulk and permanent magnet is used for magnetic supporting of the flywheel. Technical problems are also extracted of the high temperature superconducting flywheel system as an energy storage system for load leveling.
Fractal superconductivity near localization threshold
We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk 'poor conductors' in which Fermi energy E{sub F} is located in the region of localized states not so far from the Anderson mobility edge E{sub c}. We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model. Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems. We identify three distinct phases: 'critical' superconductive state formed at E{sub F} = E{sub c}, superconducting state with a strong pseudo-gap, realized due to pairing of weakly localized electrons and insulating state realized at E{sub F} still deeper inside a localized band. The 'critical' superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gapped state is the presence of two independent energy scales: superconducting gap {Delta}, that is due to many-body correlations and a new 'pseudo-gap' energy scale {Delta}{sub P} which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive T{sub c}. Two gap nature of the pseudo-gapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudo-gapped superconducting state demonstrates anomalous behavior of the optical spectral weight. The insulating state is realized due to the presence of local pairing gap but without superconducting correlations; it is characterized by a hard insulating gap in the density of single electrons and by purely activated low-temperature resistivity ln R(T) {approx} 1/T. Based on these results we propose a new 'pseudo-spin' scenario of superconductor-insulator transition and argue that it is realized in a particular class of disordered superconducting films. We conclude by the discussion of the experimental predictions of the theory and the theoretical issues that remain unsolved.
Feigel'man, M.V., E-mail: email@example.com [L.D. Landau Institute for Theoretical Physics, Kosygin st. 2, Moscow 119334 (Russian Federation); Moscow Institute of Physics and Technology, Moscow 141700 (Russian Federation); Ioffe, L.B., E-mail: firstname.lastname@example.com [L.D. Landau Institute for Theoretical Physics, Kosygin st. 2, Moscow 119334 (Russian Federation); Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States); CNRS and Universite Paris-Sud, UMR 8626, LPTMS, Orsay Cedex, F-91405 France (France); Kravtsov, V.E. [L.D. Landau Institute for Theoretical Physics, Kosygin st. 2, Moscow 119334 (Russian Federation); Abdus Salam International Center for Theoretical Physics, Trieste (Italy); Cuevas, E. [Departamento de Fisica, Universidad de Murcia, E-30071 Murcia (Spain)
Influence of hydrogen on superconducting niobium cavities
The influence of the solute hydrogen on rf properties of superconducting niobium cavities is investigated experimentally. Chemical polishing and too much electropolishing decrease the energy gap and rf breakdown fields. High-temperature vacuum firing in a UHV furnace decrease the residual loss and recovers the energy gap. Annealed cavities are, however, easily degraded not only by a short period of exposure
S. Isagawa
Photonic Band Gap resonators for high energy accelerators
We have proposed that a new type of microwave resonator, based on Photonic Band Gap (PBG) structures, may be particularly useful for high energy accelerators. We provide an explanation of the PBG concept and present data which illustrate some of the special properties associated with such structures. Further evaluation of the utility of PBG resonators requires laboratory testing of model structures at cryogenic temperatures, and at high fields. We provide a brief discussion of our test program, which is currently in progress.
Schultz, S.; Smith, D.R. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics; Kroll, N. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics]|[Stanford Linear Accelerator Center, Menlo Park, CA (United States)
Doping and critical-temperature dependence of the energy gaps in Ba(Fe1-xCox)2As2 thin films
The dependence of the superconducting gaps in epitaxial Ba(Fe1-xCox)2As2 thin films on the nominal doping x (0.04?x?0.15) was studied by means of point-contact Andreev-reflection spectroscopy. The normalized conductance curves were well fitted by using the two-dimensional Blonder-Tinkham-Klapwijk model with two nodeless, isotropic gapsŚalthough the possible presence of gap anisotropies cannot be completely excluded. The amplitudes of the two gaps ?S and ?L show similar monotonic trends as a function of the local critical temperature TcA (measured in the same point contacts) from 25 K down to 8 K. The dependence of the gaps on x is well correlated to the trend of the critical temperature, i.e., to the shape of the superconducting region in the phase diagram. When analyzed within a simple three-band Eliashberg model, this trend turns out to be compatible with a mechanism of superconducting coupling mediated by spin fluctuations, whose characteristic energy scales with Tc according to the empirical law ?0=4.65kBTc, and with a total electron-boson coupling strength ?tot=2.22 for x?0.10 (i.e., up to optimal doping) that slightly decreases to ?tot=1.82 in the overdoped samples (x=0.15).
Pecchio, P.; Daghero, D.; Ummarino, G. A.; Gonnelli, R. S.; Kurth, F.; Holzapfel, B.; Iida, K.
Orbital-selective metal-insulator transition and gap formation above TC in superconducting Rb1-xFe2-ySe2
Understanding the origin of high-temperature superconductivity in copper- and iron-based materials is one of the outstanding tasks of current research in condensed matter physics. Even the normal metallic state of these materials exhibits unusual properties. Here we report on a hierarchy of temperatures Tcsuperconducting Rb1-xFe2-ySe2 observed by THz spectroscopy (Tc=critical temperature of the superconducting phase; Tgap=temperature below which an excitation gap opens; Tmet=temperature below which a metallic optical response occurs). Above Tmet=90?K the material reveals semiconducting characteristics. Below Tmet a coherent metallic THz response emerges. This metal-to-insulator-type, orbital-selective transition is indicated by an isosbestic point in the temperature dependence of the optical conductivity and dielectric constant at THz frequencies. At Tgap=61?K, a gap opens in the THz regime and then the superconducting transition occurs at Tc=32?K. This sequence of temperatures seems to reflect a corresponding hierarchy of the electronic correlations in different bands.
Wang, Zhe; Schmidt, M.; Fischer, J.; Tsurkan, V.; Greger, M.; Vollhardt, D.; Loidl, A.; Deisenhofer, J.
Energy Gaps and Interaction Blockade in Confined Quantum Systems
We investigate universal properties of strongly confined particles that turn out to be dramatically different from what is observed for electrons in atoms and molecules. For a large class of harmonically confined systems, such as small quantum dots and optically trapped atoms, many-body particle addition and removal energies, and energy gaps, are accurately obtained from single-particle eigenvalues. Transport blockade phenomena are related to the derivative discontinuity of the exchange-correlation functional. This implies that they occur very generally, with Coulomb blockade being a particular realization of a more general phenomenon. In particular, we predict a van der Waals blockade in cold atom gases in traps.
Capelle, K. [Departamento de Fisica e Informatica, Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, 13560-970 Sao Carlos, SP (Brazil); Mathematical Physics, LTH, Lund University, 22100 Lund (Sweden); Borgh, M.; Kaerkkaeinen, K.; Reimann, S. M. [Mathematical Physics, LTH, Lund University, 22100 Lund (Sweden)
Development and operation of the JAERI superconducting energy recovery linacs
The Japan Atomic Energy Research Institute free-electron laser (JAERI FEL) group at Tokai, Ibaraki, Japan has successfully developed one of the most advanced and newest accelerator technologies named "superconducting energy recovery linacs (ERLs)" and some applications in near future using the ERLs. In the text, the current operation and high power JAERI ERL-FEL 10 kW upgrading program, ERL-light source design studies, prevention of the stainless-steel cold-worked stress-corrosion cracking failures and decommissioning of nuclear power plants in nuclear energy industries were reported and discussed briefly as a typical application of the ERL-FEL.
Minehara, Eisuke J.
Critical temperature and energy gap for the BCS equation
We derive upper and lower bounds on the critical temperature T{sub c} and the energy gap {xi} (at zero temperature) for the BCS gap equation, describing spin-(1/2) fermions interacting via a local two-body interaction potential {lambda}V(x). At weak coupling {lambda}<<1 and under appropriate assumptions on V(x), our bounds show that T{sub c}{approx}A exp(-B/{lambda}) and {xi}{approx}C exp(-B/{lambda}) for some explicit coefficients A, B, and C depending on the interaction V(x) and the chemical potential {mu}. The ratio A/C turns out to be a universal constant, independent of both V(x) and {mu}. Our analysis is valid for any {mu}; for small {mu}, or low density, our formulas reduce to well-known expressions involving the scattering length of V(x)
Hainzl, Christian; Seiringer, Robert [Departments of Mathematics and Physics, University of Alabama at Birmingham, 1300 University Boulevard, Birmingham, Alabama 35294 (United States); Department of Physics, Princeton University, Princeton, New Jersey 08542-0708 (United States)
Exporting superconductivity across the gap: Proximity effect for semiconductor valence-band states due to contact with a simple-metal superconductor
The proximity effect refers to the phenomenon whereby superconducting properties are induced in a normal conductor that is in contact with an intrinsically superconducting material. In particular, the combination of nanostructured semiconductors with bulk superconductors is of interest because these systems can host unconventional electronic excitations such as Majorana fermions when the semiconductor's charge carriers are subject to a large spin-orbit coupling. The latter requirement generally favors the use of hole-doped semiconductors. On the other hand, basic symmetry considerations imply that states from typical simple-metal superconductors will predominantly couple to a semiconductor's conduction-band states and, therefore, in the first instance generate a proximity effect for band electrons rather than holes. In this article, we show how the superconducting correlations in the conduction band are transferred also to hole states in the valence band by virtue of interband coupling. A general theory of the superconducting proximity effect for bulk and low-dimensional hole systems is presented. The interplay of interband coupling and quantum confinement is found to result in unusual wave-vector dependencies of the induced superconducting gap parameters. One particularly appealing consequence is the density tunability of the proximity effect in hole quantum wells and nanowires, which creates new possibilities for manipulating the transition to nontrivial topological phases in these systems.
Moghaddam, A. G.; Kernreiter, T.; Governale, M.; Z³licke, U.
Design optimization of superconducting magnetic energy storage coil
An optimization formulation has been developed for a superconducting magnetic energy storage (SMES) solenoid-type coil with niobium titanium (Nb-Ti) based Rutherford-type cable that minimizes the cryogenic refrigeration load into the cryostat. Minimization of refrigeration load reduces the operating cost and opens up the possibility to adopt helium re-condensing system using cryo-cooler especially for small-scale SMES system. Dynamic refrigeration load during charging or discharging operational mode of the coil dominates over steady state load. The paper outlines design optimization with practical design constraints like actual critical characteristics of the superconducting cable, maximum allowable hoop stress on winding, etc., with the objective to minimize refrigeration load into the SMES cryostat. Effect of design parameters on refrigeration load is also investigated.
Bhunia, Uttam; Saha, Subimal; Chakrabarti, Alok
Temperature dependence of the resonance and low-energy spin excitations in superconducting FeTe0.6Se0.4
We use inelastic neutron scattering to study the temperature dependence of the low-energy spin excitations in single crystals of superconducting FeTe{sub 0.6}Se{sub 0.4} (T{sub c} = 14 K). In the low-temperature superconducting state, the imaginary part of the dynamic susceptibility at the electron and hole Fermi-surfaces nesting wave vector Q = (0.5, 0.5), {chi}{sup ''} (Q, {omega}), has a small spin gap, a two-dimensional neutron spin resonance above the spin gap, and increases linearly with increasing {h_bar}{omega} for energies above the resonance. While the intensity of the resonance decreases like an order parameter with increasing temperature and disappears at temperature slightly above T{sub c}, the energy of the mode is weakly temperature dependent and vanishes concurrently above T{sub c}. This suggests that in spite of its similarities with the resonance in electron-doped superconducting BaFe{sub 2-x} (Co, Ni){sub x}As{sub 2}, the mode in FeTe{sub 0.6}Se{sub 0.4} is not directly associated with the superconducting electronic gap.
Lipscombe, O. J. [University of Tennessee, Knoxville (UTK); Luo, H.Q. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics; Lumsden, Mark D [ORNL; Dai, Pengcheng [University of Tennessee, Knoxville (UTK)
This paper demonstrates that a superconductive magnetic energy storage (SMES) system can provide a significant positive impact on electric power transmission. Through the use of SMES, transmission line loadings during heavy load hours can be reduced. Transmission losses as well as the fuel cost for these losses over a 24-hour period can also be decreased. A new SMES scheme, the SMES/dc link, is introduced in this paper for energy storage and control of power flow. The operation of this scheme and the benefits it provides are presented in this paper.
Tam, K.S.; Kumar, P. (Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (USA). Dept. of Electrical Engineering)
Study of superconducting magnetic bearing applicable to the flywheel energy storage system that consist of HTS-bulks and superconducting-coils
The Railway Technical Research Institute conducted a study to develop a superconducting magnetic bearing applicable to the flywheel energy-storage system for railways. In the first step of the study, the thrust rolling bearing was selected for application, and adopted liquid-nitrogen-cooled HTS-bulk as a rotor, and adopted superconducting coil as a stator for the superconducting magnetic bearing. Load capacity of superconducting
Hiroshi Seino; Ken Nagashima; Yoshichika Tanaka; Masahiko Nakauchi
Hybridization and superconducting gaps in heavy-fermion superconductor PuCoGa5 probed via the dynamics of photoinduced quasiparticles
We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa{sub 5}. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature T{sub c}, which speaks against phonon-mediated superconducting pairing. Upon lowering the temperature, we observe an order-of-magnitude increase of the quasiparticle relaxation time in agreement with the phonon bottleneck scenario - evidence for the presence of a hybridization gap in the electronic density of states. The modification of photoinduced reflectance in the superconducting state is consistent with the heavy character of the quasiparticles that participate in Cooper pairing. The discovery of relatively high-temperature superconductivity in the Pu-based compounds PuCoGa{sub 5} (T{sub c} = 18.5 K) and PuRhGa{sub 5} (T{sub c} = 8.7 K) has renewed the interest in actinide materials research. The Pu-based superconductors share the HoCoGa{sub 5}-type tetragonal lattice stucture with the Ce-based series of compounds (CeRhIn{sub 5}, CeCoIn{sub 5}, and CeIrIn{sub 5}) commonly referred to as '115' materials. In the Ce-based 115 compounds, CeIrIn{sub 5} (T{sub c} = 0.4 K) and CeCoIn{sub 5} (T{sub c} = 2.3 K), display superconductivity at ambient pressure. Both Ce- and Pu-based 115 compounds display the heavy fermion behavior resulting from the influence of 4f (Ce) and 5f (Pu) electrons. The most intriguing question concerns the origin of superconductivity (SC) in the 115 materials. In the Ce series, the d-wave symmetry of the SC order parameter and the proximity of SC order to magnetism have lead to a widespread belief that the unconventional SC is induced by antiferromagnetic spin fluctuations. In the Pu compounds, two possible scenarios regarding the SC mechanism have been considered: one approach favors a magnetically mediated unconventional SC similar to that in CeCoIn{sub 5}. In the other scenario, the conventional SC is mediated by phonons, where the strength of the electron-phonon (e-ph) coupling {lambda} is the crucial parameter that sets the superconducting transition temperature T{sub c}. In this Letter, we present a measurement of the e-ph coupling constant {lambda} via the pump-probe optical study of the room-temperature relaxation time of photoinduced reflectance. We find that e-ph coupling ({lambda} = 0.2-0.26) is too weak to explain the high T{sub c} of PuCoGa{sub 5} and that phonon-mediated superconductivity is unlikely in this material. Upon lowering the temperature in the normal state (T > T{sub c}), we find an order-of-magnitude increase in the relaxation time consistent with a phonon bottleneck, similar to other heavy-fermion materials, which provides the first optical evidence of the presence of a hybridization gap in the electronic density of states (DOS). Below T{sub c}, the photoinduced response exhibits dramatic changes that we ascribe to the opening of the superconducting (SC) gap at the Fermi level. The observed dynamics confirms that the same quasiparticles detected in the normal state, i.e., the heavy quasiparticles, also participate in the SC pairing. Our study is the first to directly probe the electronic structure of PuCoGa{sub 5} in the SC state and corroborate that fact. Our results are consistent with the theoretical investigations, which find that the electronic structure is dominated by cylindrical sheets of Fermi surfaces with large 5f electron character, suggesting that the delocalized 5f electrons of Pu playa key role in the superconducting pairing.
Talbayev, Diyar [Los Alamos National Laboratory; Trugman, Stuart A [Los Alamos National Laboratory; Zhu, Jian - Xin [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Kennison, John A [Los Alamos National Laboratory; Mitchell, Jeremy N [Los Alamos National Laboratory; Thompson, Joe D [Los Alamos National Laboratory; Sarrao, John L [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Burch, Kenneth S [CANADA; Chia, Elbert E. M. [CANADA
Power-law-like correlation between condensation energy and superconducting transition temperatures in iron pnictide/chalcogenide superconductors: Beyond the BCS understanding
Superconducting condensation energy U0int has been determined by integrating the electronic entropy in various iron pnictide/chalcogenide superconducting systems. It is found that U0int?Tcn with n =3-4, which is in sharp contrast to the simple BCS prediction U0BCS=1/2NF?s2, with NF the quasiparticle density of states at the Fermi energy and ?s the superconducting gap. A similar correlation holds if we compute the condensation energy through U0cal=3?neff?s2/4?2kB2, with ?neff the effective normal state electronic specific heat coefficient. This indicates a general relationship ?neff?Tcm with m =1-2, which is not predicted by the BCS scheme. A picture based on quantum criticality is proposed to explain this phenomenon.
Xing, Jie; Li, Sheng; Zeng, Bin; Mu, Gang; Shen, Bing; Schneeloch, J.; Zhong, R. D.; Liu, T. S.; Gu, G. D.; Wen, Hai-Hu
Superconductivity and the quantization of energy
Attention is presently drawn to the established fact that the innumerable interactions among the trillion or so particles of such macroscopic devices as Josephson junctions, in producing sharply defined energy levels, can be regarded as a dynamical state which is effectively divorced from environmental complexities. This degree of isolation from intrinsic perturbations has only recently been shown to be extraordinary, in light of new measurements with precision improvements of about ten orders of magnitude; these are presently evaluated in view of highly accurate results from QED and atomic spectroscopy investigations, as well as the standards of metrology.
McDonald, D. G.
Superconducting cables: Long distance energy transmission. (Latest citations from the NTIS bibliographic database). NewSearch
The bibliography contains citations concerning the design, development, and evaluation of superconducting cables and power transmission lines for long distance energy transmission. Topics include methods of cryogenic refrigeration and electrical insulation, fabrication and development of niobium alloy conductors, energy loss analysis, and dielectric design of superconducting power transmission systems. Government research reports on superconducting technology for electric power transmission and distribution are also reviewed. (Contains a minimum of 106 citations and includes a subject term index and title list.)
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Superconducting cables: Long distance energy transmission. (Latest citations from the NTIS Bibliographic database). Published Search
The bibliography contains citations concerning the design, development, and evaluation of superconducting cables and power transmission lines for long distance energy transmission. Topics include methods of cryogenic refrigeration and electrical insulation, fabrication and development of niobium alloy conductors, energy loss analysis, and dielectric design of superconducting power transmission systems. Government research reports on superconducting technology for electric power transmission and distribution are also reviewed. (Contains a minimum of 105 citations and includes a subject term index and title list.)
Superconducting cables: Long distance energy transmission. (Latest citations from the NTIS bibliographic database). Published Search
The bibliography contains citations concerning the design, development, and evaluation of superconducting cables and power transmission lines for long distance energy transmission. Topics include methods of cryogenic refrigeration and electrical insulation, fabrication and development of niobium alloy conductors, energy loss analysis, and dielectric design of superconducting power transmission systems. Government research reports on superconducting technology for electric power transmission and distribution are also reviewed.(Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)
ORNL superconducting technology program for electric energy systems
The Oak Ridge National Laboratory (ORNL) Superconducting Technology Program is conducted as part of a national effort by the US Department of Energy's (DOE's) Office of Conservation and Renewable Energy to develop the technology base needed by US industry for commercial development of electric power applications of high-temperature superconductivity. The two major elements of this program are wire development and systems development. This document describes the major research and development activities for this program together with related accomplishments. The technical progress reported was summarized from information prepared for the FY-92 Peer Review of Projects, which was conducted by DOE's Office of Program Analysis, Office of Energy Research. This ORNL program is highly leveraged by the staff and other resources of US industry and universities. Interlaboratory teams are also in place on a number of industry-driven projects. Patent disclosures, working group meetings, staff exchanges, and joint publications and presentations ensure that there is technology transfer to US industry. Working together, the collaborative teams are making tremendous progress in solving the scientific and technical issues necessary for the commercialization of long lengths of practical high-temperature superconductor wire and wire products.
Hawsey, R. A.
ORNL Superconducting Technology Program for Electric Energy Systems
The Oak Ridge National Laboratory (ORNL) Superconducting Technology Program is conducted as part of a national effort by the US Department of Energy's (DOE's) Office of Conservation and Renewable Energy to develop the technology base needed by US industry for commercial development of electric power applications of high-temperature superconductivity. The two major elements of this program are wire development and systems development. This document describes the major research and development activities for this program together with related accomplishments. The technical progress reported was summarized from information prepared for the FY 1992 Peer Review of Projects, conducted by DOE's Office of Program Analysis, Office of Energy Research. This ORNL program is highly leveraged by the staff and other resources of US industry and universities. Interlaboratory teams are also in place on a number of industry-driven projects. Patent disclosures, working group meetings, staff exchanges, and joint publications and presentations ensure that there is technology transfer to US industry. Working together, the collaborative teams are making tremendous progress in solving the scientific and technical issues necessary for the commercialization of long lengths of practical high-temperature superconductor wire and wire products.
Hawsey, R.A. (comp.)
Many body effect induced energy gap in an optically pumped graphene system
We develop a simple way to investigate the energy gap induced by many body effect in optically pumped graphene at different carrier densities. The exchange self-energy and energy dispersions are obtained analytically at the long wave limit. An energy gap depending on the carrier density is observed at the Dirac point. The energy gap induced by many body effect lies in the microwave range which is in accordance with the experimental measurements. Our theoretical results indicate that the exchange interaction via Coulomb interaction can be a mechanism to create an energy gap in optically pumped graphene.
Wei, X. F.; Wang, W. Y.; Long, M. S.; Gong, Y. P.; Liu, L. W.
Opening and reversible control of a wide energy gap in uniform monolayer graphene
For graphene to be used in semiconductor applications, a æwide energy gap' of at least 0.5?eV at the Dirac energy must be opened without the introduction of atomic defects. However, such a wide energy gap has not been realized in graphene, except in the cases of narrow, chemically terminated graphene nanostructures with inevitable edge defects. Here, we demonstrated that a wide energy gap of 0.74?eV, which is larger than that of germanium, could be opened in uniform monolayer graphene without the introduction of atomic defects into graphene. The wide energy gap was opened through the adsorption of self-assembled twisted sodium nanostrips. Furthermore, the energy gap was reversibly controllable through the alternate adsorption of sodium and oxygen. The opening of such a wide energy gap with minimal degradation of mobility could improve the applicability of graphene in semiconductor devices, which would result in a major advancement in graphene technology.
Jeon, Cheolho; Shin, Ha-Chul; Song, Inkyung; Kim, Minkook; Park, Ji-Hoon; Nam, Jungho; Oh, Dong-Hwa; Woo, Sunhee; Hwang, Chan-Cuk; Park, Chong-Yun; Ahn, Joung Real
Opening and reversible control of a wide energy gap in uniform monolayer graphene.
For graphene to be used in semiconductor applications, a 'wide energy gap' of at least 0.5?eV at the Dirac energy must be opened without the introduction of atomic defects. However, such a wide energy gap has not been realized in graphene, except in the cases of narrow, chemically terminated graphene nanostructures with inevitable edge defects. Here, we demonstrated that a wide energy gap of 0.74?eV, which is larger than that of germanium, could be opened in uniform monolayer graphene without the introduction of atomic defects into graphene. The wide energy gap was opened through the adsorption of self-assembled twisted sodium nanostrips. Furthermore, the energy gap was reversibly controllable through the alternate adsorption of sodium and oxygen. The opening of such a wide energy gap with minimal degradation of mobility could improve the applicability of graphene in semiconductor devices, which would result in a major advancement in graphene technology. PMID:24100763
Ni-impurity effects on the superconducting gap of LaCuO: Measurements of the electronic specific heat under magnetic fields
We investigate the residual ?-value of the specific heat under the magnetic field H for Ni-substituted LaCuO(x=0.15,y=0.015;Tc=26.5K) and LaCuO(x=0.15;Tc=37.0 K) crystals. The reduction of the SC gap estimated by applying the VolovikÆs relation to ?? vs. H curve is too small to explain the suppression of T in Ni-substituted samples, where ?? is the change of ? under H. We point out the possibility that T of Ni-substituted sample decreases through the reduction of the area of the coherent nodal d-wave gap in momentum space, which will play an important role in causing the superconductivity.
Kurosawa, T.; Momono, N.; Amitsuka, H.; Oda, M.; Ido, M.
Ni-impurity effects on the superconducting gap of La2-xCuO: Measurements of the electronic specific heat under magnetic fields
We investigate the residual ?-value of the specific heat under the magnetic field H for Ni-substituted LaCuO(x=0.15,y=0.015;Tc=26.5K) and LaCuO(x=0.15;Tc=37.0K) crystals. The reduction of the SC gap estimated by applying the VolovikÆs relation to ?? vs. H curve is too small to explain the suppression of T in Ni-substituted samples, where ?? is the change of ? under H. We point out the possibility that T of Ni-substituted sample decreases through the reduction of the area of the coherent nodal d-wave gap in momentum space, which will play an important role in causing the superconductivity.
Publisher's Note: Nodeless two-gap superconducting state in single crystals of the stoichiometric iron pnictide LiFeAs [Phys. Rev. B 83, 100502(R) (2011)
The variations of in- and inter- plane London penetration depths, $\\Delta\\lambda(T)$, were measured using a tunnel diode resonator in single crystals of the intrinsic pnictide superconductor LiFeAs. This compound appears to be in the clean limit with a residual resistivity of 4 ($T\\to0$) to 8 ($T_c$) $\\mu \\Omega\\cdot$cm and $RRR$ of 65 to 35, respectively. The superfluid density, $\\rho_s(T)=\\lambda^2(0)/\\lambda^2(T)$, is well described by the self-consistent two-gap $\\gamma-$model. Together with the previous data, our results support the universal evolution of the superconducting gap from nodeless to nodal upon departure from optimal doping. We also conclude that pairbreaking scattering plays an important role in the deviation of the low-temperature behavior of $\\lambda(T)$ from exponential in Fe-based compounds.
Kim, H.; Tanatar, M. A.; Song, Yoo Jang; Kwon, Yong Seung; Prozorov, R.
Maximum field capability of Energy-Saver superconducting magnets
At an energy of 1 TeV, the superconducting cable in the Energy Saver dipole magnets will be operating at approx. 96% of its nominal short sample limit; the corresponding number in the quadrupole magnets is 81%. All magnets for the Saver are individually tested for maximum current capability under two modes of operation; some 900 dipoles and 275 quadrupoles have now been measured. The dipole winding is composed of four individually wound coils. In general, the cable in the four coils comes from four different reels of cable. As part of magnet fabrication quality control, a short piece of cable from both ends of each reel has its critical current (rho = 1 x 10/sup -12/'..cap omega..-cm) measured at 5T and 4.3/sup 0/K. We present the statistical results of the maximum field tests on Saver magnets and explore the correlation with cable critical current.
Turkot, F.; Cooper, W.E.; Hanft, R.; McInturff, A.
Energy gaps in nitrogen delta-doping graphene: A first-principles study
First-principles calculations are performed to study the modulation of energy gaps in nitrogen delta-doping (N delta-doping) graphene and armchair-edge graphene nanoribbons (AGNRs). The energy gap of graphene only opens at a large nitrogen doping content. For AGNRs, the energy gaps tend to decrease with the N delta-doping, and an interesting transition from direct to indirect bandgap is observed. Moreover, the
Xiao-Lin Wei; Hui Fang; Ru-Zhi Wang; Yuan-Ping Chen; Jian-Xin Zhong
Wigner energy and shell gaps in two-nucleon separation energies
Two-nucleon separation energies are differences of binding energies. They provide important information on the relative stability of nuclei and, in particular, on shell gaps. In this work, the behavior of the decrements (change of slope) of two-nucleon separation energies has been studied. It has been shown that the bulk of this decrement at a shell-gap consists mainly of twice the difference of two effective single particle energies, plus a pairing correction. The decrement of the two-nucleon separation energies has a maximum (spike) for N=Z nuclei. A comparison with values calculated by using a seniority binding energy formula shows that the spike is due to the Wigner energy. The evolution with nuclear mass of the isospin dependence of the Wigner energy is discussed.
Gelberg, A. [Institut fuer Kernphysik, Universitaet zu Koeln, D-50937 Koeln (Germany); Institute of Physical and Chemical Research, Wako, Saitama 351-0198 (Japan); Sakurai, H. [Institute of Physical and Chemical Research, Wako, Saitama 351-0198 (Japan); Kirson, M. W. [Weizmann Institute of Science, 76100 Rehovot (Israel); Heinze, S. [Institut fuer Kernphysik, Universitaet zu Koeln, D-50937 Koeln (Germany)
The Kohn-Sham gap, the fundamental gap and the optical gap: the physical meaning of occupied and virtual Kohn-Sham orbital energies.
A number of consequences of the presence of the exchange-correlation hole potential in the Kohn-Sham potential are elucidated. One consequence is that the HOMO-LUMO orbital energy difference in the KS-DFT model (the KS gap) is not "underestimated" or even "wrong", but that it is physically expected to be an approximation to the excitation energy if electrons and holes are close, and numerically proves to be so rather accurately. It is physically not an approximation to the difference between ionization energy and electron affinity I-A (fundamental gap or chemical hardness) and also numerically differs considerably from this quantity. The KS virtual orbitals do not possess the notorious diffuseness of the Hartree-Fock virtual orbitals, they often describe excited states much more closely as simple orbital transitions. The Hartree-Fock model does yield an approximation to I-A as the HOMO-LUMO orbital energy difference (in Koopmans' frozen orbital approximation), if the anion is bound, which is often not the case. We stress the spurious nature of HF LUMOs if the orbital energy is positive. One may prefer Hartree-Fock, or mix Hartree-Fock and (approximate) KS operators to obtain a HOMO-LUMO gap as a Koopmans' approximation to I-A (in cases where A exists). That is a different one-electron model, which exists in its own right. But it is not an "improvement" of the KS model, it necessarily deteriorates the (approximate) excitation energy property of the KS gap in molecules, and deteriorates the good shape of the KS virtual orbitals. PMID:24002107
Baerends, E J; Gritsenko, O V; van Meer, R
Ni-impurity effects on the superconducting gap of La2-xSrxCuO4 studied from the magnetic field and temperature dependence of the electronic specific heat
The magnetic field and temperature dependence of the electronic specific heat Cel have been systematically investigated in La2-xSrxCu1-yNiyO4 (LSCNO) in order to study Ni-impurity effects on the superconducting (SC) gap. In LSCNO with x = 0.15 and y = 0.015, the value of ? (?Cel/T) at T = 0 K, ?0, is enhanced under the magnetic field H applied along the c axis. The increment of ?0, ??0, follows the Volovik relation ??0 = AH, characteristic of the SC gap with line nodes, with prefactor A similar to that of a pure sample. The Cel/T versus T curve under H = 0 shows a d-wave-like SC anomaly with an abrupt increase at Tc and T-linear dependence at T ? Tc, although the ?0-value in the Cel/T versus T curve increases with increasing Ni concentrations. Interestingly, as the SC part of Cel/T, Cel/T - ?0 ? ?s, decreases in LSCNO, Tc is reduced in proportion to the decrease of ?s. These findings can be explained phenomenologically by a simple model in which Ni impurities bring about strong pair breaking at the edges of the coherent nodal part of the Fermi surface but in the vicinity of the nodes of the SC gap. The reduction of the SC condensation energy U0 in LSCNO, evaluated from Cel at T?Tc, is also understood by the same model.
Kurosawa, T.; Momono, N.; Oda, M.; Ido, M.
Survey of domestic research on superconducting magnetic energy storage
This report documents the results of a survey of domestic research on superconducting magnetic energy storage (SMES) undertaken with the support of the Oak Ridge National Laboratory (ORNL) Superconductivity Pilot Center. Each survey entry includes the following: Name, address, and other telephone and facsimile numbers of the principal investigator and other staff members; funding for fiscal year 1991, 1992, 1993; brief descriptions of the program, the technical progress to date, and the expected technical progress; a note on any other collaboration. Included with the survey are recommendations intended to help DOE decide how best to support SMES research and development (R&D). To summarize, I would say that important elements of a well-rounded SMES research program for DOE are as follows. (1) Construction of a large ETM. (2) Development of SMES as an enabling technology for solar and wind generation, especially in conjunction with the ETM program, if possible. (3) Development of small SMES units for electric networks, for rapid transit, and as noninterruptible power supplies [uses (2), (3), and (4) above]. In this connection, lightweight, fiber-reinforced polymer structures, which would be especially advantageous for space and transportation applications, should be developed. (4) Continued study of the potential impacts of high-temperature superconductors on SMES, with construction as soon as feasible of small SMES units using high-temperature superconductors (HTSs).
Dresner, L.
This report documents the results of a survey of domestic research on superconducting magnetic energy storage (SMES) undertaken with the support of the Oak Ridge National Laboratory (ORNL) Superconductivity Pilot Center. Each survey entry includes the following: Name, address, and other telephone and facsimile numbers of the principal investigator and other staff members; funding for fiscal year 1991, 1992, 1993; brief descriptions of the program, the technical progress to date, and the expected technical progress; a note on any other collaboration. Included with the survey are recommendations intended to help DOE decide how best to support SMES research and development (R D). To summarize, I would say that important elements of a well-rounded SMES research program for DOE are as follows. (1) Construction of a large ETM. (2) Development of SMES as an enabling technology for solar and wind generation, especially in conjunction with the ETM program, if possible. (3) Development of small SMES units for electric networks, for rapid transit, and as noninterruptible power supplies (uses (2), (3), and (4) above). In this connection, lightweight, fiber-reinforced polymer structures, which would be especially advantageous for space and transportation applications, should be developed. (4) Continued study of the potential impacts of high-temperature superconductors on SMES, with construction as soon as feasible of small SMES units using high-temperature superconductors (HTSs).
Competition between the pseudogap and superconductivity in cuprates
The relationship between the pseudogap and superconductivity is one of the central issues in physics of cuprates. By studying the spectral weights associated with pseudogap and superconductivity by angle resolved photoemission spectroscopy (ARPES) we found that there is a direct correlation between the loss of the low energy spectral weight due to the opening of the pseudogap and a decrease of the spectral weight associated with superconductivity as a function of momentum and doping. We therefore conclude that the pseudogap competes with the superconductivity by depleting the spectral weight available for pairing in the region of momentum space, where the superconducting gap is largest.
Kaminski, Adam
Superconducting magnetic energy storage (SMES) program, January 1-December 31, 1981
Work reported is on the development of a 30 MJ superconducting magnetic energy storage (SMES) unit for use by the Bonneville Power Administration (BPA) to stabilize power oscillations on their Pacific AC Intertie. The 30 MJ superconducting coil manufacture was completed. Design of the seismic mounting of the coil to the nonconducting dewar lid and a concrete foundation is complete. The superconducting application VAR (SAVAR) control study indicated a low economic advantage and the SAVAR program was terminated. An economic and technological evaluation of superconducting fault current limiter (SFCL) was completed and the results are reported.
Rogers, J.D. (comp.)
Breakdown of the energy gap law in molecular lanthanoid luminescence: the smallest energy gap is not universally relevant for nonradiative deactivation.
For several decades, the energy gap law has been the prevalent theoretical framework for the discussion of nonradiative deactivation of lanthanoid luminescence in molecular coordination chemistry. Here we show experimentally on samarium and dysprosium model complexes that the size of the energy gap ?E between a lanthanoid emitting state and the next-lower electronic state cannot be considered a reliable and accurate predictor of the quantitative extent of nonradiative deactivation by aromatic C-H and C-D oscillator overtones. Because the energy gap is the central pillar for the entire conceptual framework of the energy gap law, this finding amounts to largely invalidating this theory for the quantitative description of molecular multiphonon relaxation. PMID:24665884
Doffek, Christine; Wahsner, Jessica; Kreidt, Elisabeth; Seitz, Michael
As part of the Superconducting Magnetic Energy Storage/Engineering Test Model (SMES-ETM) program, design, analysis, fabrication and test programs were conducted to evaluate the low cost manufacturing of Fiberglass Reinforced Plastic (FRP) beams for usage as major components of the structural and electrical insulation systems. These studies utilized pultrusion process technologies and vinylester resins to produce large net sections at costs significantly below that of conventional materials. Demonstration articles incorporating laminate architectures and design details representative of SMES-ETM components were fabricated using the pultrusion process and epoxy, vinylester, and polyester resin systems. The mechanical and thermal properties of these articles were measured over the temperature range from 4 K to 300 K. The results of these tests showed that the pultruded, vinylester components have properties comparable to those of currently used materials, such as G-10, and are capable of meeting the design requirements for the SMES-ETM system.
Rix, Craig; McColskey, David; Acree, Robert
As part of the Superconducting Magnetic Energy Storage/Engineering Test Model (SMES-ETM) programs, design, analysis, fabrication and test programs were conducted to evaluate the low cost manufacturing of Fiberglass Reinforced Plastic (FRP) beams for usage as major components of the structural and electrical insulation systems. These studies utilized pultrusion process technologies and vinylester resins to produce large net sections at costs significantly below that of conventional materials. Demonstration articles incorporating laminate architectures and design details representative of SMES-ETM components were fabricated using the pultrusion process and epoxy, vinylester, and polyester resin systems. The mechanical and thermal properties of these articles were measured over the temperature range from 4 K to 300 K. The results of these tests showed that the pultruded, vinylester components have properties comparable to those of currently used materials, such as G-10, and are capable of meeting the design requirements for the SMES-ETM system.
Rix, C. (General Dynamics Space Magnetics, San Diego, CA (United States)); McColskey, D. (National Inst. of Standards and Technology, Boulder, CO (United States)); Acree, R. (Phillips Lab., Edwards Air Force Base, CA (United States))
Effect of out-of-plane disorder on superconducting gap anisotropy in Bi2+xSr2-xCaCu2O8+? as seen via Raman spectroscopy
We report a systematic study of the variation of electronic Raman spectra as a function of disorder for Bi2+xSr2-xCaCu2O8+? with different Bi:Sr nonstoichiometry. We have observed that, with increasing disorder, the suppression of the superconducting gap is observed only in the nodal region, while there is no change in the antinodal gap. This dichotomy of the response to disorder in the nodal and the antinodal gap can be interpreted as evidence for different origins of these two gaps.
Murai, N.; Masui, T.; Ishikado, M.; Ishida, S.; Eisaki, H.; Uchida, S.; Tajima, S.
Superconducting cascade electron refrigerator
The design and operation of an electronic cooler based on a combination of superconducting tunnel junctions is described. The cascade extraction of hot-quasiparticles, which stems from the energy gaps of two different superconductors, allows for a normal metal to be cooled down to about 100 mK starting from a bath temperature of 0.5 K. We discuss the practical implementation, potential performance, and limitations of such a device.
Camarasa-G¾mez, M.; Di Marco, A.; Hekking, F. W. J.; Winkelmann, C. B.; Courtois, H.; Giazotto, F.
Application of Superconducting Magnet Energy Storage to Power System Stabilizing Control.
The application of Superconducting Magnet Energy Storage (SMES) to the stabilizing control of power systems with a long distance bulk power transmission line and with longitudinal interconnected structure is presented. Control schemes for stabilization us...
Y. Mitani K. Tsuji Y. Murakami
Design and Construction of a Resistive Energy Dump Device for Bipolar Superconducting Magnet Systems.
When superconducting magnets quench, the resistance of the conductor material rises rapidly to its normal value. This increase in resistance can result in catastrophic heating in the magnet unless stored field energy is quickly removed from the system. Ph...
M. J. Mohan
Temperature-dependent far-infrared reflectance of La-Sr-Cu-O and La-Ca-Cu-O: Bardeen-Cooper-Schrieffer electrodynamics but uncertain energy gap
The available far-infrared data for polycrystalline La-Sr-Cu-O and La-Ca-Cu-O show a reflectance edge with energy near 2.5k/sub B/T/sub c/. This edge has been variously interpreted as the onset of absorption due to an energy gap, and as a low-frequency plasma edge caused by strong far-infrared resonances. Our measured temperature dependence of the reflectance edge closely fits the temperature dependence of the order parameter in a mean-field theory, and hence is consistent with the energy-gap hypothesis. In this paper, we construct a model dielectric function for La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ which is consistent with mean-field theory and the hypothesis of a plasma edge. We find that the temperature dependence of the plasma frequency in this model also closely fits the measured temperature dependence of the reflectance edge. Furthermore, both hypotheses accurately predict the experimentally observed temperature dependence of the absorption at frequencies much less than the reflectance edge. This observation has significant implications for the construction of fast low-loss superconducting devices. We conclude that the electrodynamics of the superconducting transition in La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ are well described by a Bardeen-Cooper-Schrieffer-like mean-field theory. However, given the identical predictions of the energy-gap and plasma-edge hypotheses, it is premature to deduce a precise value for the magnitude of the energy gap from the infrared data.
Sherwin, M.S.; Richards, P.L.; Zettl, A.
Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits
The origin of magnetic flux noise in dc Superconducting Quantum Interference Devices (SQUIDs) with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 25 years. This noise limits both the low frequency performance of SQUIDs and the decoherence time of flux-sensitive superconducting qubits, making scaling-up for quantum computing problematic. Recent calculations and experiments indicate that the noise is generated by electrons that randomly reverse their spin directions. Their areal density of ś 5 x 10^17 m-2 is relatively insensitive to the nature of the superconductor and substrate. Here, we propose that the local magnetic moments originate in metal-induced gap states (MIGSs) localized by potential disorder at the metal-insulator interface. MIGSs are particularly sensitive to such disorder, so that the localized states have a Coulomb repulsion sufficiently large to make them singly occupied. Our calculations demonstrate that a modest level of disorder generates the required areal density of localized moments. This result suggests that magnetic flux noise could be reduced by fabricating superconductor-insulator interfaces with less disorder. Support: NSF DMR07-05941, US DOE De-AC02-05CH11231, Samsung Foundation, Teragrid, NERSC.
Choi, Sangkook; Lee, Dung-Hai; Louie, Steven G.; Clarke, John
Superconducting gamma and fast-neutron spectrometers with high energy resolution
Superconducting Gamma-ray and fast-neutron spectrometers with very high energy resolution operated at very low temperatures are provided. The sensor consists of a bulk absorber and a superconducting thermometer weakly coupled to a cold reservoir, and determines the energy of the incident particle from the rise in temperature upon absorption. A superconducting film operated at the transition between its superconducting and its normal state is used as the thermometer, and sensor operation at reservoir temperatures around 0.1 K reduces thermal fluctuations and thus enables very high energy resolution. Depending on the choice of absorber material, the spectrometer can be configured either as a Gamma-spectrometer or as a fast-neutron spectrometer.
Friedrich, Stephan (San Jose, CA); , Niedermayr, Thomas R. (Oakland, CA); Labov, Simon E. (Berkeley, CA)
Enhanced energy relaxation process of a quantum memory coupled to a superconducting qubit
For quantum information processing, each physical system has a different advantage as regards implementation, so hybrid systems that benefit from the advantage of several systems would provide a promising approach. One common hybrid approach involves combining a superconducting qubit as a controllable qubit and another quantum system with a long coherence time as a memory qubit. The use of a superconducting qubit gives us excellent controllability of the quantum states, and the memory qubit is capable of storing information for a long time. It has been believed that selective coupling can be realized between a superconducting qubit and a memory qubit by tuning the energy splitting between them. However, we have shown that this detuning approach has a fundamental drawback as regards energy leakage from the memory qubit. Even if the superconducting qubit is effectively separated by reasonable detuning, a non-negligible incoherent energy relaxation in the memory qubit occurs via residual weak coupling when the superconducting qubit is affected by severe dephasing. This energy transport from the memory qubit to the control qubit can be interpreted as the appearance of the anti-quantum Zeno effect induced by the fluctuation in the superconducting qubit. We also discuss possible ways to avoid this energy relaxation process, which is feasible with existing technology.
Matsuzaki, Yuichiro; Nakano, Hayato
Superconductivity, cohesive energy density, and electron-atom ratio in metals
It is shown that superconductivity above 8 K occurs in alloys and metallic compounds within relatively narrow regions of cohesive energy density with a sharp peak which includes Nb3Ge, SiV3, Nb3Ga, and NbN. When cross-correlated with the electron-atom ratio, high-temperature superconductivity can be observed in only a few regions. This suggests a search for superconductors with high-transition temperatures and critical fields within these regions.
England, C.; Lawson, D. D.; Hrubes, J. D.
Graphene field effect transistor without an energy gap
Graphene is a room temperature ballistic electron conductor and also a very good thermal conductor. Thus, it has been regarded as an ideal material for postsilicon electronic applications. A major complication is that the relativistic massless electrons in pristine graphene exhibit unimpeded Klein tunneling penetration through gate potential barriers. Thus, previous efforts to realize a field effect transistor for logic applications have assumed that introduction of a band gap in graphene is a prerequisite. Unfortunately, extrinsic treatments designed to open a band gap seriously degrade device quality, yielding very low mobility and uncontrolled on/off current ratios. To solve this dilemma, we propose a gating mechanism that leads to a hundredfold enhancement in on/off transmittance ratio for normally incident electrons without any band gap engineering. Thus, our saw-shaped geometry gate potential (in place of the conventional bar-shaped geometry) leads to switching to an off state while retaining the ultrahigh electron mobility in the on state. In particular, we report that an on/off transmittance ratio of 130 is achievable for a sawtooth gate with a gate length of 80 nm. Our switching mechanism demonstrates that intrinsic graphene can be used in designing logic devices without serious alteration of the conventional field effect transistor architecture. This suggests a new variable for the optimization of the graphene-based deviceŚgeometry of the gate electrode.
Jang, Min Seok; Kim, Hyungjun; Son, Young-Woo; Atwater, Harry A.; Goddard, William A.
Hybrid fuel cell and energy storage systems using superconducting coil or batteries for clean electricity generation
This paper described a novel design of a hybrid fuel cell and energy storage system using high temperature superconducting energy storage system (HT-SMES) or batteries to meet fast changing load. The power electronic switches in the converter of the energy storage system are controlled in such a way that the amplitude and waveform of the inverter output current from the
Darmawan Sutanto; Kai Ding
Design and cost of a utility scale superconducting magnetic energy storage plant
Superconducting Magnetic Energy Storage (SMES) has potential as a viable technology for use in electric utility load leveling. The advantage of SMES over other energy storage technologies is its high net roundtrip energy efficiency. This paper reports the major features and costs of a jointly developed 5000 MWh SMES plant design.
Loyd, R.J.; Nakamura, T.; Schoenung, S.M.; Lieurance, D.W.; Hilal, M.A.; Rogers, J.D.; Purcell, J.R.; Hassenzahl, W.V.
Superconducting Magnetic Energy Storage and other large-scale SDI cryogenic applications programs
The paper describes the Superconducting Magnetic Energy Storage (SMES) program for terrestrial storage of energy for use in powering ground-based directed energy weapons. Special attention is given to SMES technology for SDI applications, the components of a SMES system, the SMES Engineering Test Model Development Program, and the SMES critical technologies. It is pointed out that SMES has applications other
Richard L. Verga
Energy transfer in bichromophoric molecules: The effect of symmetry and donor/acceptor energy gap
The dependence of the rate of singlet excitation transfer on the donor-acceptor energy gap was investigated in bichromophoric spiranes with symmetry-forbidden zero-order electronic coupling. The fluorescence measurements were performed in a supersonic jet in order to avoid collisional and inhomogeneous line broadening. Fluorescence excitation spectra and single-vibronic-level emission spectra of the model chromophores cyclopentaphenanthrene and 1,8-dimethylnaphthalene and the bichromophores spirofluorenephenanthrene and spirofluorenanaphthalene are presented and analyzed. Although the transition moments of the linked chromophores are rigorously perpendicular and the exchange coupling between the {upsilon}{prime} = 0 states is computationally shown to be zero, all spiranes with energy gaps larger than {approximately}1000 cm{sup {minus}1} exhibited complete electronic energy transfer from all vibrational states of the electronically excited donor, including the undistorted {upsilon}{prime} = 0 state. This behavior is explained in terms of vibronic coupling between the sparse states of the donor and the dense manifold (pseudocontinuum) of the acceptor states. The electronic energy transfer was sufficiently fast to result in measurable lifetime broadening of the donor absorption lines, from which the k{sub EET} was estimated. The results demonstrate that the zero-order picture overestimates the degree of the molecular orbital symmetry control over electronic energy transfer and charge-transfer rates and that at sufficiently high driving forces the vibronically meditated symmetry-forbidden electronic energy transfer can be very rapid ({approximately}1 {times} 10{sup 12} s{sup {minus}1}).
Yip, W.T.; Levy, D.H. [Univ. of Chicago, IL (United States)] [Univ. of Chicago, IL (United States); Kobetic, R.; Piotrowiak, P. [Rutgers Univ., Newark, NJ (United States). Dept. of Chemistry] [Rutgers Univ., Newark, NJ (United States). Dept. of Chemistry
Physical Content of the Exact Kohn-Sham Orbital Energies: Band Gaps and Derivative Discontinuities
The local-density approximation for the exchange-correlation potential understimates the fundamental band gaps of semiconductors and insulators by about 40%. It is argued here that underestimation of the gap width is also to be expected from the unknown exact potential of Kohn-Sham density-functional theory, because of derivative discontinuities of the exchange-correlation energy. The need for an energy-dependent potential in band theory
John P. Perdew; Mel Levy
Development of an Abort Gap Monitor for High-Energy Proton Rings
The fill pattern in proton synchrotrons usually features an empty gap, longer than the abort kicker raise time, for machine protection. This gap is referred to as the ``abort gap,'' and any particles, which may accumulate in it due to injection errors and diffusion between RF buckets, would be lost inside the ring, rather than in the beam dump, during the kicker firing. In large proton rings, due to the high energies involved, it is vital to monitor the build up of charges in the abort gap with a high sensitivity. We present a study of an abort gap monitor based on a photomultiplier with a gated microchannel plate, which would allow for detecting low charge densities by monitoring the synchrotron radiation emitted. We show results of beam test experiments at the Advanced Light Source using a Hamamatsu 5916U MCP-PMT and compare them to the specifications for the Large Hadron Collider.
Beche, J.-F.; Byrd, J.; de Santis, S.; Denes, P.; Placidi, M.; Turner, W.; Zolotorev, M.
The paper describes the Superconducting Magnetic Energy Storage (SMES) program for terrestrial storage of energy for use in powering ground-based directed energy weapons. Special attention is given to SMES technology for SDI applications, the components of a SMES system, the SMES Engineering Test Model Development Program, and the SMES critical technologies. It is pointed out that SMES has applications other than SDI, such as the commercial electric utility industry and space power systems, including hydrogen-cooled cryoconductors, superconducting turboalternators, and high-temperature superconductor power leads.
Verga, Richard L.
Basic Research Needs for Superconductivity. Report of the Basic Energy Sciences Workshop on Superconductivity, May 8-11, 2006
As an energy carrier, electricity has no rival with regard to its environmental cleanliness, flexibility in interfacing with multiple production sources and end uses, and efficiency of delivery. In fact, the electric power grid was named ?the greatest engineering achievement of the 20th century? by the National Academy of Engineering. This grid, a technological marvel ingeniously knitted together from local networks growing out from cities and rural centers, may be the biggest and most complex artificial system ever built. However, the growing demand for electricity will soon challenge the grid beyond its capability, compromising its reliability through voltage fluctuations that crash digital electronics, brownouts that disable industrial processes and harm electrical equipment, and power failures like the North American blackout in 2003 and subsequent blackouts in London, Scandinavia, and Italy in the same year. The North American blackout affected 50 million people and caused approximately $6 billion in economic damage over the four days of its duration. Superconductivity offers powerful new opportunities for restoring the reliability of the power grid and increasing its capacity and efficiency. Superconductors are capable of carrying current without loss, making the parts of the grid they replace dramatically more efficient. Superconducting wires carry up to five times the current carried by copper wires that have the same cross section, thereby providing ample capacity for future expansion while requiring no increase in the number of overhead access lines or underground conduits. Their use is especially attractive in urban areas, where replacing copper with superconductors in power-saturated underground conduits avoids expensive new underground construction. Superconducting transformers cut the volume, weight, and losses of conventional transformers by a factor of two and do not require the contaminating and flammable transformer oils that violate urban safety codes. Unlike traditional grid technology, superconducting fault current limiters are smart. They increase their resistance abruptly in response to overcurrents from faults in the system, thus limiting the overcurrents and protecting the grid from damage. They react fast in both triggering and automatically resetting after the overload is cleared, providing a new, self-healing feature that enhances grid reliability. Superconducting reactive power regulators further enhance reliability by instantaneously adjusting reactive power for maximum efficiency and stability in a compact and economic package that is easily sited in urban grids. Not only do superconducting motors and generators cut losses, weight, and volume by a factor of two, but they are also much more tolerant of voltage sag, frequency instabilities, and reactive power fluctuations than their conventional counterparts. The challenge facing the electricity grid to provide abundant, reliable power will soon grow to crisis proportions. Continuing urbanization remains the dominant historic demographic trend in the United States and in the world. By 2030, nearly 90% of the U.S. population will reside in cities and suburbs, where increasingly strict permitting requirements preclude bringing in additional overhead access lines, underground cables are saturated, and growth in power demand is highest. The power grid has never faced a challenge so great or so critical to our future productivity, economic growth, and quality of life. Incremental advances in existing grid technology are not capable of solving the urban power bottleneck. Revolutionary new solutions are needed ? the kind that come only from superconductivity.
Sarrao, J.; Kwok, W-K; Bozovic, I.; Mazin, I.; Seamus, J. C.; Civale, L.; Christen, D.; Horwitz, J.; Kellogg, G.; Finnemore, D.; Crabtree, G.; Welp, U.; Ashton, C.; Herndon, B.; Shapard, L.; Nault, R. M.
Enhanced Andreev reflection in gapped graphene
We theoretically demonstrate unusual features of superconducting proximity effect in gapped graphene that presents a pseudospin symmetry-broken ferromagnet with a net pseudomagnetization. We find that the presence of a band gap makes the Andreev conductance of graphene superconductor/pseudoferromagnet (S/PF) junction to behave similar to that of a graphene ferromagnet-superconductor junction. The energy gap ?N can enhance the pseudospin inverted Andreev conductance of S/PF junction to reach a limiting maximum value for ?N??, which depending on the bias voltage can be larger than the value for the corresponding junction with no energy gap. We further demonstrate a damped-oscillatory behavior for the local density of states of the PF region of S/PF junction and a long-range crossed Andreev reflection process in PF/S/PF structure with antiparallel alignment of pseudomagnetizations of PFs, which confirm that, in this respect, the gapped normal graphene behaves like a ferromagnetic graphene.
Majidi, Leyla; Zareyan, Malek
Sensing with superconducting point contacts.
Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the superconducting energy gap, superconductors provide ultrahigh sensitivities for high resolution spectroscopies. The so-called Andreev reflection process between normal metal and superconductor carries complex and rich information which can be utilized as powerful sensor when fully exploited. In this review, we would discuss recent experimental and theoretical developments in the supercurrent transport through superconducting point contacts and their relevance to sensing applications, and we would highlight their current issues and potentials. A true utilization of the method based on Andreev reflection analysis opens up possibilities for a new class of ultrasensitive sensors. PMID:22778630
Nurbawono, Argo; Zhang, Chun
Sensing with Superconducting Point Contacts
Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the superconducting energy gap, superconductors provide ultrahigh sensitivities for high resolution spectroscopies. The so-called Andreev reflection process between normal metal and superconductor carries complex and rich information which can be utilized as powerful sensor when fully exploited. In this review, we would discuss recent experimental and theoretical developments in the supercurrent transport through superconducting point contacts and their relevance to sensing applications, and we would highlight their current issues and potentials. A true utilization of the method based on Andreev reflection analysis opens up possibilities for a new class of ultrasensitive sensors.
Optical studies of gap, exchange, and hopping energies in the insulating cuprates
We have measured the insulating energy gap ? and the exchange interaction J in a series of cuprate crystals, including T'-phase M2CuO4 (M=Pr, Nd, Sm, Eu, and Gd), T*-phase La,Tb,Sr2CuO4, and T-phase La2CuO4. We find that the energy gap scales predominantly with the in-plane Cu-O distance, scaling as ? log?/ ? logd~-6. Furthermore, contrary to simple expectations, the energy gap increases with decreasing Cu-O distance, suggesting that Coulomb and other repulsive energies dominate the effects of band hybridization. Using a three-band Hubbard-model expression, our studies of ? and J in the cuprates allow us to estimate that the hopping energy t scales with Cu-O distance as ? logt/? logd~-4.
Cooper, S. L.; Thomas, G. A.; Millis, A. J.; Sulewski, P. E.; Orenstein, J.; Rapkine, D. H.; Cheong, S.-W.; Trevor, P. L.
Superconducting RF cavities and magnets for a 4-TeV energy muon collider.
The accelerators must take the muon beams from approximately 100 MeV to 2 TeV energies within the muon lifetime for a 4 TeV energy muon collider. These constraints plus the muon decay heating seriously challenge the designs of the superconducting RF (SRF)...
Q. S. Shu M. Green D. Neuffer D. Summers S. Simrock
Electroluminescence at silicon band gap energy from mechanically pressed indium-tin-oxide/Si contact
Room temperature electroluminescence (EL) corresponding to Si band gap energy is observed from mechanically pressed indium-tin-oxide (ITO)/Si contact. The intensity of luminescence is pressure dependent and highly related to the current-voltage characteristics. Increasing pressure simultaneously reduces the rectification property and the luminescence. The physical reason for EL is attributed to the formation of an air gap between the ITO and the Si substrate. The role of the air gap is similar to the oxide layer in the metal-oxide-semiconductor structure. The influence of surface quality of the Si substrate on the luminescence spectrum is also studied, and found to be significant.
Lin, Ching-Fuh; Chen, Miin-Jang; Chang, Shu-Wei; Chung, Peng-Fei; Liang, Eih-Zhe; Su, Ting-Wien; Liu, C. W.
Kinetic energy driven superfluidity and superconductivity and the origin of the Meissner effect
Superfluidity and superconductivity have many elements in common. However, I argue that their most important commonality has been overlooked: that both are kinetic energy driven. Clear evidence that superfluidity in 4He is kinetic energy driven is the shape of the ? transition and the negative thermal expansion coefficient below T?. Clear evidence that superconductivity is kinetic energy driven is the Meissner effect: I argue that otherwise the Meissner effect would not take place. Associated with this physics I predict that superconductors expel negative charge from the interior to the surface and that a spin current exists in the ground state of superconductors (spin Meissner effect). I propose that this common physics of superconductors and superfluids originates in rotational zero point motion. This view of superconductivity and superfluidity implies that rotational zero-point motion is a fundamental property of the quantum world that is missed in the current understanding.
Hirsch, J. E.
Fully gapped superconductivity in Ni-pnictide superconductors BaNi2As2 and SrNi2P2
We have performed low-temperature specific heat C and thermal conductivity {kappa} measurements on the Ni-pnictide superconductors BaNi{sub 2}As{sub 2} (T{sub c} = 0.7K) and SrNi{sub 2}P{sub 2} (T{sub c} = 1.4K). The temperature dependences C(T) and {kappa}(T) of the two compounds are similar to the results of a number of s-wave superconductors. Furthermore, the concave field responses of the residual {kappa} for BaNi{sub 2}As{sub 2} rules out the presence of nodes on the Fermi surfaces. We postulate that fully gapped superconductivity could be universal for Ni-pnictide superconductors. Specific heat data on Ba{sub 0.6}La{sub 0.4}Ni{sub 2}As{sub 2} shows a mild suppression of Tc and H{sub c2} relative to BaNi{sub 2}As{sub 2}.
Kurita, N [Los Alamos National Laboratory (LANL); Ronning, F. [Los Alamos National Laboratory (LANL); Miclea, C. F. [Los Alamos National Laboratory (LANL); Tokiwa, Y. [Los Alamos National Laboratory (LANL); Bauer, E. D. [Los Alamos National Laboratory (LANL); Subedi, Alaska P [ORNL; Singh, David J [ORNL; Sakai, H [Japan Atomic Energy Agency (JAEA); Thompson, J. D. [Los Alamos National Laboratory (LANL); Movshovich, R [Los Alamos National Laboratory (LANL)
Molecular gap and energy level diagram for pentacene adsorbed on filled d-band metal surfaces
The authors present a combined photoemission and scanning-tunneling spectroscopy study of the filled electronic states, the molecular energy gap, and the energy level diagram of highly ordered arrays of pentacene deposited on the Cu(119) vicinal surface. The states localized at the interface are clearly singled out, comparing the results at different pentacene thicknesses and with gas-phase photoemission data. The molecular gap of 2.35 eV, the hole injection barrier of 1.05 eV, and the electron injection barrier of 1.30 eV determine the energy level diagram of the states localized at the pentacene molecules.
Baldacchini, Chiara; Mariani, Carlo; Betti, Maria Grazia; Gavioli, L.; Fanetti, M.; Sancrotti, M.
A wideband vibration energy harvester based on a folded asymmetric gapped cantilever
This paper reports a wideband multi-mass multi-spring piezoelectric vibration energy harvester (VEH) based on a folded asymmetric gapped cantilever, which enables multiple resonant modes formed by pure bending of every stage. Moreover, the heaviest proof mass is placed at the last stage of the cantilever to increase the harvested power. The VEH's energy conversion efficiency is further increased using the asymmetric gapped structure. A prototype has been developed and characterized. The experimental results match with finite element simulation well. The prototype was tested on an air conditioning unit to demonstrate its energy harvesting capability with a realistic broadband vibration source.
Hu, Yating; Xu, Yong
Determination of the Temperature Dependence of the Band Gap Energy of Semiconductors from Transmission Spectra
A method to determine the temperature dependence of the band gap energy, E g( T), of semiconductors from their measured transmission spectra is described. A relationship between the band gap energy and the energy corresponding to the peak of the spectral derivative is found for InAs and validated for III-V and II-VI binary semiconductors (InAs, InP, GaAs, GaP, ZnSe, and CdTe). Band gap energies obtained using this method are within 1% of previously published results over a temperature range of 80 K to 650 K. The same method was also applied to two bulk ternary semiconductor alloys (In x Ga1- x As and InAs1- y P y ) for several compositions. Predicted results compared well with thin-film measurements available in the literature. A separate technique for determining E g is also reported, using thickness-dependent transmission spectra. Finally, the thermooptic coefficient (d n/d T) is determined using the derivative of the band gap energy with respect to temperature (d E g/d T) and is compared with direct experimental measured results.
Wei, Jean; Murray, Joel M.; Barnes, Jacob; Gonzalez, Leonel P.; Guha, Shekhar
Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1-xCox)2As2
Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe0.955Co0.045)2As2 (Tc = 8 K) and for three overdoped samples Ba(Fe1-xCox)2As2 (x = 0.103, 0.13, and 0.15; Tc = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat ? (?C/T as T ? 0, i.e., a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys ? ? H0.5▒0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ? 10 T) data show a Volovik-like behavior of ? ? H0.3-0.4, followed by an inflection point, followed at higher fields by ? ? H1. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.
Kim, J. S.; Faeth, B. D.; Wang, Y.; Hirschfeld, P. J.; Stewart, G. R.; Gofryk, K.; Ronning, F.; Sefat, A. S.; Choi, K. Y.; Kim, K. H.
Energy Flow for a Variable-Gap Capacitor
When capacitor plates are separated, the capacitor's electrostatic energy either increases or decreases, depending upon whether the charge or the voltage is held constant. For the constant-voltage case, an interesting puzzle can be posed to students: How is it possible that an external agent does positive work on the capacitor while at the same time the capacitor's stored energy decreases? An energy flow diagram, as suggested by Art Hobson's TPT article,1 helps to visualize the movements of energy among different parts of the system. What Richard Feynman calls a ``surprising factor of one-half'' in the expression for the force between capacitor plates confronts students with an additional puzzle to decipher.2
Greene, Nathaniel R.
Rugged superconducting detector for monitoring infrared energy sources in harsh environments
Broadband electromagnetic characterization of hot plasmas, such as in nuclear fusion reactors and related experiments, requires detecting systems that must withstand high flux of particles and electromagnetic radiations. We propose a rugged layout of a high temperature superconducting detector aimed at 3 THz collective Thomson scattering (CTS) spectroscopy in hot fusion plasma. The YBa2Cu3O7 - x superconducting film is patterned by standard photolithography and the sensing area of the device is created by means of high-energy heavy ion irradiation, in order to modify the crystal structure both of the superconducting film and of the substrate. This method diminishes process costs and resulting device fragility due to membrane or air-bridge structures that are commonly needed for MIR and FIR radiation detection. Moreover the sensing area of the device is wired by the same superconducting material and thus excellent mechanical strength is exhibited by the whole device, due to the oxide substrate. Continuous wave operation of prototype devices is demonstrated at liquid nitrogen temperature, for selected infrared spectra of broadband thermal energy sources. Several solutions, which exploit the advantages coming from the robustness of this layout in terms of intrinsic radiation hardness of the superconducting material and of the needed optical components, are analysed with reference to applications of infrared electromagnetic detectors in a tokamak machine environment.
Laviano, F.; Gerbaldo, R.; Ghigo, G.; Gozzelino, L.; Minetti, B.; Rovelli, A.; Mezzetti, E.
Energy-gap reduction in heavily doped silicon: Causes and consequences
The authors review briefly the existing theoretical treatments of the various effects that contribute to the reduction of the energy gap in heavily doped Si, namely electron-electron and electron-impurity interactions and the effect of disorder in the impurity distribution. They then turn to the longstanding question why energy-gap reductions extracted from three different types of experiments have persistently produced values with substantial discrepancies, making it impossible to compare with theoretical values. First, they demonstrate that a meaningful comparison between theory and experiment can indeed be made if theoretical calculations are carried out for actual quantities that experiments measure, e.g. luminescence spectra, as recently done by Selloni and Pantelides. Then, they demonstrate that, independent of any theoretical calculations, the optical absorption spectra are fully consistent with the luminescence spectra and that the discrepancies in the energy-gap reductions extracted from the two sets of spectra are caused entirely by the curve-fitting procedures used in analyzing optical-absorption data. Finally, they show explicitly that, as already believed by many authors, energy-gap reductions extracted from electrical measurements on transistors do not correspond to true gap reductions. They identify two corrections that must be added to the values extracted from the electrical data in order to arrive at the true gap reductions and show that the resulting values are in good overall agreement with luminescence and absorption data. They, therefore, demonstrate that the observed reduction in emitter injection efficiency in bipolar transistors is not strictly due to a gap reduction, as generally believed, but to three very different effects.
Pantelides, Sokrates T.; Selloni, Annabella; Car, Roberto
Estimating the Energy Gap Among US Children: A Counterfactual Approach
OBJECTIVE. Our goal was to quantify the magnitude of energy imbalance responsible for the increase in body weight among US children during the periods 1988 -1994 and 1999 -2002. METHODS. We adopted a counterfactual approach to estimate weight gains in excess of normal growth and the implicit \\
Y. Claire Wang; Steven L. Gortmaker; Arthur M. Sobol; Karen M. Kuntz
Modeling US Adult Obesity Trends: A System Dynamics Model for Estimating Energy Imbalance Gap.
Objectives. We present a system dynamics model that quantifies the energy imbalance gap responsible for the US adult obesity epidemic among gender and racial subpopulations. Methods. We divided the adult population into gender-race/ethnicity subpopulations and body mass index (BMI) classes. We defined transition rates between classes as a function of metabolic dynamics of individuals within each class. We estimated energy intake in each BMI class within the past 4 decades as a multiplication of the equilibrium energy intake of individuals in that class. Through calibration, we estimated the energy gap multiplier for each gender-race-BMI group by matching simulated BMI distributions for each subpopulation against national data with maximum likelihood estimation. Results. No subpopulation showed a negative or zero energy gap, suggesting that the obesity epidemic continues to worsen, albeit at a slower rate. In the past decade the epidemic has slowed for non-Hispanic Whites, is starting to slow for non-Hispanic Blacks, but continues to accelerate among Mexican Americans. Conclusions. The differential energy balance gap across subpopulations and over time suggests that interventions should be tailored to subpopulations' needs. PMID:24832405
Fallah-Fini, Saeideh; Rahmandad, Hazhir; Huang, Terry T-K; Bures, Regina M; Glass, Thomas A
Modeling US Adult Obesity Trends: A System Dynamics Model for Estimating Energy Imbalance Gap
Objectives. We present a system dynamics model that quantifies the energy imbalance gap responsible for the US adult obesity epidemic among gender and racial subpopulations. Methods. We divided the adult population into gender¢race/ethnicity subpopulations and body mass index (BMI) classes. We defined transition rates between classes as a function of metabolic dynamics of individuals within each class. We estimated energy intake in each BMI class within the past 4 decades as a multiplication of the equilibrium energy intake of individuals in that class. Through calibration, we estimated the energy gap multiplier for each gender¢race¢BMI group by matching simulated BMI distributions for each subpopulation against national data with maximum likelihood estimation. Results. No subpopulation showed a negative or zero energy gap, suggesting that the obesity epidemic continues to worsen, albeit at a slower rate. In the past decade the epidemic has slowed for non-Hispanic Whites, is starting to slow for non-Hispanic Blacks, but continues to accelerate among Mexican Americans. Conclusions. The differential energy balance gap across subpopulations and over time suggests that interventions should be tailored to subpopulationsÆ needs.
Rahmandad, Hazhir; Huang, Terry T.-K.; Bures, Regina M.; Glass, Thomas A.
Bulk limit of superconducting condensation energy in 2D Hubbard model
We have studied the possibility of superconductivity (SC) in the titled model by computing the SC condensation energy per site as the energy gain in the d-pairing SC state using the variational Monte Carlo method. Its bulk limit was obtained by finite-size scaling with approximately fixed electron density ?. This value survived finite for ??0.84 when next n.n. transfer energy
K. Yamaji; T. Yanagisawa; S. Koike
Energy gap in the aetiology of body weight gain and obesity: a challenging concept with a complex evaluation and pitfalls.
The concept of energy gap(s) is useful for understanding the consequence of a small daily, weekly, or monthly positive energy balance and the inconspicuous shift in weight gain ultimately leading to overweight and obesity. Energy gap is a dynamic concept: an initial positive energy gap incurred via an increase in energy intake (or a decrease in physical activity) is not constant, may fade out with time if the initial conditions are maintained, and depends on the 'efficiency' with which the readjustment of the energy imbalance gap occurs with time. The metabolic response to an energy imbalance gap and the magnitude of the energy gap(s) can be estimated by at least two methods, i.e. i) assessment by longitudinal overfeeding studies, imposing (by design) an initial positive energy imbalance gap; ii) retrospective assessment based on epidemiological surveys, whereby the accumulated endogenous energy storage per unit of time is calculated from the change in body weight and body composition. In order to illustrate the difficulty of accurately assessing an energy gap we have used, as an illustrative example, a recent epidemiological study which tracked changes in total energy intake (estimated by gross food availability) and body weight over 3 decades in the US, combined with total energy expenditure prediction from body weight using doubly labelled water data. At the population level, the study attempted to assess the cause of the energy gap purported to be entirely due to increased food intake. Based on an estimate of change in energy intake judged to be more reliable (i.e. in the same study population) and together with calculations of simple energetic indices, our analysis suggests that conclusions about the fundamental causes of obesity development in a population (excess intake vs. low physical activity or both) is clouded by a high level of uncertainty. PMID:24457473
Schutz, Yves; Byrne, Nuala M; Dulloo, Abdul; Hills, Andrew P
Smoothing control of wind power generator output by superconducting magnetic energy storage system
This paper proposes a system composed of a wind turbine generator system (WTGS) and superconducting magnetic energy storage (SMES) unit, in which SMES is controlled for smoothing the wind generator output power. A determination of power capacity of SMES unit which is sufficient for the smoothing control but as small as possible is very important problem. In this paper, an
Tomoki Asao; Rion Takahashi; Toshiaki Murata; Junji Tamura; Masahiro Kubo; Akira Kuwayama; Takatoshi Matsumoto
Capacitor Energy Needed to Induce Transitions from the Superconducting to the Normal State.
The purpose of this paper is to describe a technique to turn a long length of superconducting wire normal by dumping a charged capacitor into it and justify some formulae needed in the design. The physical phenomenon is described. A formula for the energy...
P. H. Eberhard R. R. Ross
Development of a low energy particle detector using a superconducting transition edge sensor
It is possible for a superconductive transition edge sensor (TES) to detect directly the low energy proton generated in the neutron beta decay. The precision measurement of the proton spectrum is important to test the prediction of the Standard Model of electroweak interaction. Therefore, we are developing a TES microcalorimeter with a large effective area for a proton detector. Our
Masashi Ohno; Hiromi Sato; Tokihiro Ikeda; Hirohiko M. Shimizu
Application of superconducting magnet energy storage to improve power system dynamic performance
The application of superconducting magnet energy storage (SMES) to the stabilization of a power system with long-distance bulk power transmission lines which has the problem of poorly damped power oscillations is presented. Control schemes for stabilization using SMES capable of controlling active and reactive power simultaneously in four quadrant ranges are proposed. The effective locations and the necessary capacities of
Y. Mitani; K. Tsuji; Y. Murakami
Superconducting magnetic energy storage: A key technology for the 21st century
Superconducting magnetic energy storage (SMES), a solid state system, is most efficient in round-trip efficiency and in providing instantaneous response to demand. SMES can help electric utilities moderate variations between customer demand requirements and generation load. SMES can conserve fossil fuels through increased system efficiencies, thus providing economic and environmental benefits. SMES can store electricity from intermittent renewable resources and
Dynamic simulation of hybrid wind-diesel power generation system with superconducting magnetic energy storage
In this paper, a systematic method of choosing the gain parameter of the wind turbine generator pitch control is presented, using the Lyapunov technique, that guarantees stability. A comprehensive digital computer model of a hybrid wind-Diesel power generation system, including the Diesel and wind power dynamics with a superconducting magnetic energy storage (SMES) unit, for stability evaluation is developed. The
S. C. Tripathy
Concepts of Flywheels for Energy Storage Using Autostable High-T(Sub C) Superconducting Magnetic Bearings.
A flywheel for energy storage using autostable high-T(sub c) superconducting magnetic bearings has been built. The rotating disk has a total weight of 2.8 kg. The maximum speed is 9240 rpm. A process that allows accelerated, reliable and reproducible prod...
H. J. Bornemann R. Zabka P. Boegler C. Urban H. Rietschel
Analysis of superconducting magnetic energy storage applications at a proposed wind farm site near Browning, Montana.
A computer program was developed to analyze the viability of integrating superconducting magnetic energy storage (SMES) with proposed wind farm scenarios at a site near Browning, Montana. The program simulated an hour-by-hour account of the charge/dischar...
K. L. Gaustad J. G. De Steese
Superconducting Magnetic Energy Storage (SMES) Program. Progress Report, January 1-December 31, 1984.
The 30 MJ, 10 MW superconducting magnetic energy storage (SMES) system was devised to interact in the Western US Power System as an alternate means to damp unstable oscillations at 0.35 Hz on the Pacific HVAC Intertie. The SMES unit was installed at the T...
Four quadrant multilevel current source power conditioning for superconductive magnetic energy Storage
The main purpose of this paper is to describe advances in high current source converter (CSC) and control for use in superconductive magnetic energy storage (SMES) schemes instead of the conventional PWM-chopper based VSC configurations. The multi-level current reinjection (MLCR) CSC provides the simplest structure, as well as switching at zero current, a property that permits retaining the use of
N. J. Murray; J. Arrillaga; N. R. Watson; Y. H. Liu
Superconducting magnetic energy storage (SMES) for industrial applications-comparison with battery systems
The authors have considered using a superconducting coil to store energy as an impulsive high power supply for industrial applications such as smoothing of short power interruptions, and smoothing of varying load. They present the results of an economic and technical evaluation of such a system for two applications. The applications are (1) as substitution for the flywheels of the
P. G. Therond; I. Joly; M. Volker
Excitation of Superconducting Qubits from Hot Nonequilibrium Quasiparticles
Superconducting qubits probe environmental defects such as nonequilibrium quasiparticles, an important source of decoherence. We show that ōhotö nonequilibrium quasiparticles, with energies above the superconducting gap, affect qubits differently from quasiparticles at the gap, implying qubits can probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we predict a non-negligible increase in the qubit excited state probability Pe. By injecting hot quasiparticles into a qubit, we experimentally measure an increase of Pe in semiquantitative agreement with the model and rule out the typically assumed thermal distribution.
Wenner, J.; Yin, Yi; Lucero, Erik; Barends, R.; Chen, Yu; Chiaro, B.; Kelly, J.; Lenander, M.; Mariantoni, Matteo; Megrant, A.; Neill, C.; O'Malley, P. J. J.; Sank, D.; Vainsencher, A.; Wang, H.; White, T. C.; Cleland, A. N.; Martinis, John M.
Concepts of flywheels for energy storage using autostable high-T(sub c) superconducting magnetic bearings
A flywheel for energy storage using autostable high-T(sub c) superconducting magnetic bearings has been built. The rotating disk has a total weight of 2.8 kg. The maximum speed is 9240 rpm. A process that allows accelerated, reliable and reproducible production of melt-textured superconducting material used for the bearings has been developed. In order to define optimum configurations for radial and axial bearings, interaction forces in three dimensions and vertical and horizontal stiffness have been measured between superconductors and permanent magnets in different geometries and various shapes. Static as well as dynamic measurements have been performed. Results are being reported and compared to theoretical models.
Bornemann, Hans J.; Zabka, R.; Boegler, P.; Urban, C.; Rietschel, H.
Capital and operating cost estimates for high temperature superconducting magnetic energy storage
Capital and operating costs have been estimated for mid-scale (2 to 200 Mwh) superconducting magnetic energy storage (SMES) designed to use high temperature superconductors (HTS). Capital costs are dominated by the cost of superconducting materials. Operating costs, primarily for regeneration, are significantly reduced for HTS-SMES in comparison to low temperature, conventional systems. This cost component is small compared to other O and M and capital components, when levelized annual costs are projected. In this paper, the developments required for HTS-SMES feasibility are discussed.
Schoenung, S.M.; Meier, W.R. (Schafer (W.J.) Associates, Inc., Pleasanton, CA (United States)); Fagaly, R.L.; Heiberger, M.; Stephens, R.B.; Leuer, J.A.; Guzman, R.A. (General Atomics Co., San Diego, CA (United States))
Magnetic resonant mode in the low-energy spin-excitation spectrum of superconducting Rb2Fe4Se5 single crystals.
We have studied the low-energy spin-excitation spectrum of the single-crystalline Rb(2)Fe(4)Se(5) superconductor (T(c)=32 K) by means of inelastic neutron scattering. In the superconducting state, we observe a magnetic resonant mode centered at an energy of ??(res)=14 meV and at the (0.5 0.25 0.5) wave vector (unfolded Fe-sublattice notation), which differs from the ones characterizing magnetic resonant modes in other iron-based superconductors. Our finding suggests that the 245-iron selenides are unconventional superconductors with a sign-changing order parameter, in which bulk superconductivity coexists with the ?5ū?5 magnetic superstructure. The estimated ratios of ??(res)/k(B)T(c)?5.1▒0.4 and ??(res)/2??0.7▒0.1, where ? is the superconducting gap, indicate moderate pairing strength in this compound, similar to that in optimally doped 1111 and 122 pnictides. PMID:22107568
Park, J T; Friemel, G; Li, Yuan; Kim, J-H; Tsurkan, V; Deisenhofer, J; Krug von Nidda, H-A; Loidl, A; Ivanov, A; Keimer, B; Inosov, D S
Probable observation of ½excitonic╗ superconductivity in formvar-aluminum sandwiches
SummaryĀĀThe Ginzburg's ½generalized jellium╗ model of the proximity effect in superconductor-dielectric systems is tested against\\u000a a wide phenomenology occurring in formvar-metal multilayers. The experimental evidence gained from enhanced superconductivity,\\u000a critical magnetic fields, energy gap and pair-breaking parameter values seems to support the hypothesis that a formvar eigenfrequency\\u000a plays the same role as the Debye frequency in setting up the superconductivity
N. A. Mancini; G. Giaquinta; G. Burrafato; C. Di Mauro; A. Pennisi; F. Simone; S. O. Troia
Band-gap energy and electron effective mass of polycrystalline Zn3N2
Zn3N2 polycrystalline films with n+-type conductivity have been grown by metalorganic chemical vapor deposition and rf-molecular beam epitaxy with carrier concentration in the range between 1019 and ~1020 cm-3. Oxygen contamination without an intentional doping was found to be a cause of high electron concentration, leading to a larger band-gap energy due to Burstein-Moss shift. The significant blue shift of the optical band gap Eopt with increasing carrier concentration ne obeys the relation Eopt=1.06+1.30ū10-14ne2/3. This evaluation enables the conclusion that the actual band-gap energy of Zn3N2 is 1.06 eV. Electron effective mass m* for Zn3N2 has been deduced from Fourier transform infrared reflectivity measurements to be (0.29+/-0.05)mo.
Suda, Toshikazu; Kakishita, Kazuhiko
Erbium energy levels relative to the band gap of gadolinium oxide
Undoped and Er 3+ doped Gd 2O 3 single crystal fibers were prepared by the laser heated pedestal growth (LHPG) method. The absorption and emission spectra of the samples were studied. The band gap of Gd 2O 3 crystal is found at 5.2 eV. A two-step photoconductivity measurement was designed to determine the Er 3+ energy level position relative to the host band gap. The lowest Er 3+ 4f-5d transition energy (5.93 eV) exceeds the host band gap. By measuring the photoconductivity induced from an excited state to the 5d bands, the Er 3+ ground state is found to be 0.7▒0.2 eV below the valence band.
Jia, D.; Lu, L.; Yen, W. M.
30-MJ superconducting magnetic energy storage for electric-transmission stabilization
The Bonneville Power Administration operates the electric power transmission system that connects the Pacific Northwest and southern California. The HVAC interties develop 0.35 Hz oscillations when the lines are heavily loaded. A 30 MJ (8.4 kWh) Superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter can provide system damping for the oscillation. The unit is scheduled for installation in 1982 and operation in 1982-83. Status of the project is described. The conductor has been fully tested electrically and mechanically and the 5 kA superconducting cable has been produced. The 30 MJ superconducting coil is essentially complete. All major components of the electrical and cryogenic systems except the nonconducting dewar have been completed. The refrigerator and converter are undergoing tests. The system is to be located at the BPA Tacoma Substation and operated by microwave link from Portland, OR.
Turner, R.D.; Rogers, J.D.
A bi-annular-gap magnetorheological energy absorber for shock and vibration mitigation
For semi-active shock and vibration mitigation systems using magnetorheological energy absorbers (MREAs), the minimization of the field-off damper force of the MREA at high speed is of particular significance because the damper force due to the viscous damping at high speed becomes too excessive and thus the controllable dynamic force range that is defined by the ratio of the field-on damper force to the field-off damper force is significantly reduced. In this paper, a bi-annular-gap MREA with an inner-set permanent magnet is proposed to decrease the field-off damper force at high speed while keeping appropriate dynamic force range for improving shock and vibration mitigation performance. In the bi-annular-gap MREA, two concentric annular gaps are configured in parallel so as to decrease the baseline damper force and both magnetic activation methods using the electromagnetic coil winding and the permanent magnet are used to keep holding appropriate magnetic intensity in these two concentric annular gaps in the consideration of failure of the electric power supply. An initial field-on damper force is produced by the magnetic field bias generated from the inner-set permanent magnet. The initial damper force of the MREA can be increased (or decreased) through applying positive (or negative) current to the electromagnetic coil winding inside the bi-annular-gap MREA. After establishing the analytical damper force model of the bi-annular-gap MREA using a Bingham-plastic nonlinear fluid model, the principle and magnetic properties of the MREA are analytically validated and analyzed via electromagnetic finite element analysis (FEA). The performance of the bi-annular-gap MREA is also theoretically compared with that of a traditional single-annular- gap MREA with the constraints of an identical volume by the performance matrix, such as the damper force, dynamic force range, and Bingham number with respect to different excitation velocities.
Bai, Xian-Xu; Wereley, Norman M.; Choi, Young-Tai; Wang, Dai-Hua
Nuclear energy gap calculations using realistic and delta-function forces
Energy gap calculations are made with the realistic Yale-Shakin interaction and the standard delta -function interaction. States below the valence shell are taken into account. It is found that the results are very close, showing that they are practically insensitive to the details of the interaction. The constant- Delta approximation is found to be very well justified.
M. C. Jain; Y. R. Waghmare
Velocity-dependent energy gaps and dynamics of superfluid neutron stars
We show that suppression of the baryon energy gaps, caused by the relative motion of superfluid and normal liquid components, can substantially influence dynamical properties and evolution of neutron stars. This effect has been previously ignored in the neutron star literature.
Gusakov, M. E.; Kantor, E. M.
Concerning the superconducting gap symmetry in YBa?Cu?O?- ?, YBa?Cu?O, and La? - xSrxCuO? determined from muon spin rotation in mixed states of crystals and powders.
Muon spin rotation (?(+)SR) measurements of square-root second moments of local magnetic fields ? in superconducting mixed states, as published for oriented crystals and powder samples of YBa(2)Cu(3)O(7 - ?) (??0.05), YBa(2)Cu(4)O(8) and La(2 - x)Sr(x)CuO(4) (x ? 0.15-0.17), are subjected to comparative analysis for superconducting gap symmetry. For oriented crystals it is shown that anomalous dependences of ? on temperature T and applied field H, as-measured and extracted a- and b-axial components, are attributable to fluxon depinning and disorder that obscure the intrinsic character of the superconducting penetration depth. Random averages derived from oriented crystal data differ markedly from corresponding non-oriented powders, owing to the weaker influence of pinning in high-quality crystals. Related indicators for pinning perturbations, such as non-monotonic H dependence of ?, irreproducible data and strong H dependence of apparent transition temperatures, are also evident. Strong intrinsic pinning suppresses thermal anomalies in c-axis components of ?, which reflect nodeless gap symmetries in YBa(2)Cu(3)O(7 - ?) and YBa(2)Cu(4)O(8). For YBa(2)Cu(3)O(7 - ?), the crystal (a-b components, corrected for depinning) and powder data all reflect a nodeless gap (however, a-b symmetries remain unresolved for crystalline YBa(2)Cu(4)O(8) and La(1.83)Sr(0.17)CuO(4)). Inconsistencies contained in multiple and noded gap interpretations of crystal data, and observed differences between bulk ?(+)SR and surface-sensitive measurements are discussed. PMID:21778567
Harshman, Dale R; Fiory, Anthony T
Concerning the superconducting gap symmetry in YBa2Cu3O7 - ?, YBa2Cu4O8, and La2 - xSrxCuO4 determined from muon spin rotation in mixed states of crystals and powders
Muon spin rotation (?+SR) measurements of square-root second moments of local magnetic fields ? in superconducting mixed states, as published for oriented crystals and powder samples of YBa2Cu3O7 - ? (??0.05), YBa2Cu4O8 and La2 - xSrxCuO4 (x ~ 0.15-0.17), are subjected to comparative analysis for superconducting gap symmetry. For oriented crystals it is shown that anomalous dependences of ? on temperature T and applied field H, as-measured and extracted a- and b-axial components, are attributable to fluxon depinning and disorder that obscure the intrinsic character of the superconducting penetration depth. Random averages derived from oriented crystal data differ markedly from corresponding non-oriented powders, owing to the weaker influence of pinning in high-quality crystals. Related indicators for pinning perturbations, such as non-monotonic H dependence of ?, irreproducible data and strong H dependence of apparent transition temperatures, are also evident. Strong intrinsic pinning suppresses thermal anomalies in c-axis components of ?, which reflect nodeless gap symmetries in YBa2Cu3O7 - ? and YBa2Cu4O8. For YBa2Cu3O7 - ?, the crystal (a-b components, corrected for depinning) and powder data all reflect a nodeless gap (however, a-b symmetries remain unresolved for crystalline YBa2Cu4O8 and La1.83Sr0.17CuO4). Inconsistencies contained in multiple and noded gap interpretations of crystal data, and observed differences between bulk ?+SR and surface-sensitive measurements are discussed.
Harshman, Dale R.; Fiory, Anthony T.
Superconductivity under a ferromagnetic molecular field
Superconductivity under a ferromagnetic molecular field is investigated theoretically based on a one-dimensional electron-band model. By using an exact solution which takes into account infinite numbers of higher harmonics for the Bogoliubov-de Gennes equation, it is demonstrated that the spatially modulated superconducting state with a distorted sinusoidal wave is stabilized in the highfield region. A key feature of the solution is a soliton lattice structure which has a two-energy-gap structure and is accompanied by a spin-density polarization of the conduction electrons. The coexistence phase observed in ErRh4B4 which consists of ferromagnetism, superconductivity, and a sinusoidally modulated magnetic state, is successfully interpreted in terms of this modulated superconducting state.
Machida, Kazushige; Nakanishi, Hiizu
Design and manufacture of a high temperature superconducting magnetic energy storage device
Micro-Superconducting Magnetic Energy Storage (?-SMES) technology has emerged as a method for mitigating voltage sags for smaller scale applications using energy storage capacities of less than 100kJ. These units are designed to mitigate low frequency (<1kHz) voltage sags in power distribution systems extending the lifetime of electronic loads by reducing voltage fluctuations and reducing load outages due to under-voltage trips.
Christopher John Hawley
Phase competition in trisected superconducting dome
A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials, such as the cuprate high-temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates, where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping- and temperature-dependence ARPES study of spectral gaps in Bi2Sr2CaCu2O8+?, covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p = 0.19 for the pseudogap phase and p = 0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below Tc and exists p > 0.19 at higher temperatures. Our data imply a revised phase diagram that reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.
Vishik, I. M.; Hashimoto, M.; He, Rui-Hua; Lee, Wei-Sheng; Schmitt, Felix; Lu, Donghui; Moore, R. G.; Zhang, C.; Meevasana, W.; Sasagawa, T.; Uchida, S.; Fujita, Kazuhiro; Ishida, S.; Ishikado, M.; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Hussain, Zahid; Devereaux, Thomas P.; Shen, Zhi-Xun
The optical band gap and surface free energy of polyethylene modified by electron beam irradiations
In this study, investigations have been carried out on electron beam irradiated ultra high molecular weight polyethylene (UHMWPE). Polyethylene samples were irradiated with 1.5 MeV electron beam at doses ranging from 50 to 500 kGy. Modifications in optical properties and photoluminescence behavior of the polymer were evaluated by UV-vis and photoluminescence techniques. Changes of surface layer composition of UHMWPE produced by electron irradiations were studied by Rutherford back scattering spectrometry (RBS). The change in wettability and surface free energy induced by irradiations was also investigated. The optical absorption studies reveal that both optical band gap and Urbach's energy decreases with increasing electron dose. A correlation between energy gap and the number of carbon atoms in clusters is discussed. Photoluminescence spectra were reveal remarkable decrease in the integrated luminescence intensity with increasing irradiation dose. Contact angle measurements showed that wettability and surface free energy increases with increasing the irradiation dose.
Abdul-Kader, A. M.
Introduction to progress and promise of superconductivity for energy storage in the electric power sector
Around the world, many groups conduct research, development and demonstration (RD and D) to make storage an economic option for the electric power sector. The progress and prospects for the application of superconductivity, with emphasis on high-temperature superconductivity, to the electric power sector has been the topic of an IEA Implementing Agreement, begun in 1990. The present Task members are Canada, Denmark, Finland, Germany, Israel, Italy, Japan, Korea, the Netherlands, Norway, Sweden, Switzerland, Turkey, the United Kingdom and the US. As a result of the Implementing Agreement, work has been done by the Operating Agent with the full participation of all the member countries. This work has facilitated the exchange of informtion among experts in all countries and has documented relevant assessments. Further, this work has reviewed the status of SMES and is now updating same, as well as investigating the progress on and prospects for flywheels with superconducting bearings. The Operating Agent and Task members find a substantially different set of opportunities for and alternatives to storage than was the case before the 1987 discovery of high-temperature superconductivity. Beside the need to level generation, there is also the need to level the load on transmission lines, increase transmission stability, and increase power quality. These needs could be addressed by high power storage that could be brought in and out of the grid in fractions of a second. Superconducting Magnetic Energy Storage and flywheels with superconducting bearings are devices that deserve continued RD and D because they promise to be the needed storage devices.
Wolsky, A.M.
Photoreflectance Investigations of Temperature Dependence of the ``Different'' Energy Gaps in GaInNAs Compounds
In this paper, we report photoreflectance investigations of GaInNAs layers almost lattice-matched to GaAs substrate and annealed at different temperatures. Our investigations done from 10 K to room temperature give evidence that these layers exhibit several distinct band gaps. These distinct band gaps, which were found to co-exist, are associated with different nitrogen bonding configurations (N-Ga4-mInm (0<= m <=4) short-range-order clusters). The annealing-induced blueshift of GaInNAs band gap energy, which is usually observed in this system, is due to the change in the intensity of PR resonances related to different N-Ga4-mInm configurations.
Kudrawiec, R.; Misiewicz, J.; Pavelescu, E.-M.; Konttinen, J.; Pessa, M.
Temperature dependence of the energy gap and spin-orbit splitting in a narrow-gap InGaAsSb solid solution
Temperature dependence of the energy gap and the spin-orbit split off transition in a thick layer of narrow-gap InGaAsSb material with high In content has been determined by a combination of photoluminescence and photoreflectance. The respective temperature coefficients have been found to be equal for both the transitions and determined to be ? = -0.41 meV/K. For the investigated In0.86Ga0.14As0.83Sb0.17 alloy, the separation energy of the split-off band has been obtained to be ?so = 0.460 eV and experimentally evidenced to be independent on temperature, which opens broad application prospects for these multinary (multicomponent) narrow gap compounds and their heterostructures.
Motyka, M.; Janiak, F.; Sek, G.; Misiewicz, J.; Moiseev, K. D.
Energy Band Gap Behavior as a Function of Optical Electronegativity for Semiconducting and Insulating Binary Oxides
A relationship between energy band gap and electronegativity has long been understood to exist. However, defining the relationship between the two for binary oxide systems has proven difficult. Many scientists tried to model the band gap as a function of Pauling electronegativity values, but we show that by using a new concept called ``optical electronegativity'' one can obtain much better predictions regarding band gaps of new oxide. Interestingly we found that the behavior of oxides varies across depending on the chemical group the cation is from. With that knowledge, we developed two equations to describe the alkali earth metal and poor metal oxide. By using our models, we are able to predict the band gap of radium oxide at 5.36 eV. Due to the contributions of `d' and `f' orbitals we could not model lanthanide rare earth and transition metal oxides but rather we found that band gaps for both lay beween 3.56 - 5.72 eV, and 1.82 -- 3.82 eV, respectively.
Dagenais, Kristen; Chamberlin, Matthew; Constantin, Costel
Factors responsible for the stability and the existence of a clean energy gap of a silicon nanocluster
We present a critical theoretical study of electronic properties of silicon nanoclusters, in particular the roles played by symmetry, relaxation, and hydrogen passivation on the stability, the gap states and the energy gap of the system using the order N [O(N)] nonorthogonal tight-binding molecular dynamics and the local analysis of electronic structure. We find that for an unrelaxed cluster with its atoms occupying the regular tetrahedral network, the presence of undistorted local bonding configuration is sufficient for the appearance of a small clean energy gap. However, the energy gap of the unrelaxed cluster does not start at the highest occupied molecular orbital (HOMO). In fact, between the HOMO and the lower edge of the energy gap, localized dangling bond states are found. With hydrogen passivation, the localized dangling bond states are eliminated, resulting in a wider and clean energy gap. Relaxation of these hydrogen passivated clusters does not alter either the structure or the energy gap appreciably. However, if the silicon clusters are allowed to relax first, the majority of the dangling bonds are eliminated but additional defect states due to bond distortion appear, making the energy gap dirty. Hydrogen passivation of these relaxed clusters will further eliminate most of the remnant dangling bonds but no appreciable effect on the defect states associated with bond distortions will take place, thus still resulting in a dirty gap. For the hydrogen-passivated Si{sub N} nanoclusters with no bond distortion and no overall symmetry, we have studied the variation of the energy gap as a function of size of the cluster for N in the range of 80energy gap on the size shows similar behavior to that for silicon nanoclusters with no bond distortion but possessing overall symmetry.
Liu, Lei; Jayanthi, C. S.; Wu, Shi-Yu
Quantification of the energy gap in young overweight children. The PIAMA birth cohort study
BackgroundĀĀOverweight develops gradually as a result of a long term surplus on the balance between energy intake and energy expenditure.\\u000a Aim of this study was to quantify the positive energy balance responsible for excess body weight gain (energy gap) in young\\u000a overweight children.\\u000a \\u000a \\u000a \\u000a \\u000a MethodsĀĀReported data on weight and height were used of 2190 Dutch children participating in the PIAMA birth
Saskia W van den Berg; Jolanda MA Boer; Salome Scholtens; Johan C de Jongste; Bert Brunekreef; Henriette A Smit; Alet H Wijga
Band gap energy and optical transitions in polyenes formed by thermal decomposition of polyvinyl alcohol
The band gap of the ensemble of oligoene clusters formed by thermocatalytic decomposition of polyvinyl alcohol is parametrized using optical absorption spectra. A band gap energy of E gm =1.53 ▒ 0.02 eV at the end of an infinite polyene chain is found by extrapolating the energies of ? ? ?* transitions in clusters with a number of double bonds varying from 4 to 12. This value is close to the band gap of trans-polyacetylene and the lower bound for the Tauc energy E gT =1.50 eV, which characterizes the minimum interband transition energy. E gT is essentially independent of the concentration of oligoene clusters, which is determined by the concentration of the AlCl3 thermal decomposition catalyst. The Urbach energy determined from the long wavelength edge of the spectrum falls from 2.21 to 0.66 eV as the AlCl3 concentration is raised from 11.1 to 41.7 mmol per mol of polyvinyl alcohol structural units.
Kulak, A. I.; Bondarava, G. V.; Shchurevich, O. A.
Energiespeicherung in supraleitenden Spulen (SMES). Ergebnisse einer Technikfolgenabschaetzung. (Superconducting magnetic energy storage (SMES). Results of a technology assessment).
The authors report on results of a Technology Assessment study commissioned by the German Federal Ministry of Education, Science, Research and Technology. The objective of this study was to evaluate the potential of superconducting magnetic energy storage...
T. Fleischer K. P. Juengst V. Brandl W. Maurer E. Nieke
Specific Heat To Hc2: Evidence for Nodes or Deep Minima in the Superconducting Gap of Under- and Overdoped BaFe2-xCoxAs2
Low temperature specific heat, C, in magnetic fields up to Hc2 is reported for BaFe1.91Co0.09As2 (underdoped, Hc2 16 T, Tc=8 K), BaFe1.79Co0.21As2 (overdoped, Hc2 27 T, Tc=17 K), and - for comparison - BaFe1.95Ni0.05As2, which should have properties similar to the underdoped Co-sample. Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials respectively. The present work shows that the measured behavior of the specific heat ? ( C/T as T->0, i. e. a measure of the electronic density of states at the Fermi energy) as a function of field obeys ? H^0.6▒0.1, similar to the Volovik effect for nodal superconductors, over the entire field range for both under- and overdoped Co samples as well as for the underdoped Ni sample. By comparison to theory, the possibility of two bands, one with line nodes and one fully gapped, being present in these materials is discussed.
Stewart, G. R.; Kim, J. S.; Gofryk, K.; Ronning, F.; Sefat, A. S.; Choi, K. Y.; Kim, K. H.
CW Superconducting RF Photoinjector Development for Energy Recovery Linacs
ERLs have the powerful potential to provide very high current beams with exceptional and tailored parameters for many applications, from next-generation light sources to electron coolers. However, the demands placed on the electron source are severe. It must operate CW, generating a current of 100 mA or more with a normalized emittance of order 1 {micro}m rad. Beyond these requirements, issues such as dark current and long-term reliability are critical to the success of ERL facilities. As part of the BERLinPro project, Helmholtz Zentrum Berlin (HZB) is developing a CWSRF photoinjector in three stages, the first of which is currently being installed at HZB's HoBiCaT facility. It consists of an SRF-cavity with a Pb cathode and a superconducting solenoid. Subsequent development stages include the integration of a high-quantum-efficiency cathode and RF components for high-current operation. This paper discusses the first stage towards an ERL-suitable SRF photoinjector, the present status of the facility and first cavity tests.
Neumann A.; Rao T.; Anders, W.; Dirsat, M.; Frahm, A. Jankowiak, A.; Kamps, T.; Knobloch, J.; Kugeler, O.; Quast, T.; Rudolph, J.; Schenk, M.; Schuster, M.; Smedley, J.; Sekutowicz, J.; Kneisel, P.; Nietubyc, R.; Will, I.
The influence of the solute hydrogen on rf properties of superconducting niobium cavities is investigated experimentally. Chemical polishing and too much electropolishing decrease the energy gap and rf breakdown fields. High-temperature vacuum firing in a UHV furnace decrease the residual loss and recovers the energy gap. Annealed cavities are, however, easily degraded not only by a short period of exposure to hydrogen, but also by a long term storage in air. Chemically polished cavities also show a great enhancement of the penetration depth ?0. These effects can be ascribed to hydrogen which is picked up from etchants or from atmosphere.
Isagawa, S.
Energy-resolved detection of single infrared photons with ? = 8 ?m using a superconducting microbolometer
We report on the detection of single photons with ? = 8 ?m using a superconducting hot-electron microbolometer. The sensing element is a titanium transition-edge sensor with a volume ~0.1 ?m3 fabricated on a silicon substrate. Poisson photon counting statistics including simultaneous detection of 3 photons was observed. The width of the photon-number peaks was 0.11 eV, 70% of the photon energy, at 50-100 mK. This achieved energy resolution is one of the best figures reported so far for superconducting devices. Such devices can be suitable for single-photon calorimetric spectroscopy throughout the mid-infrared and even the far-infrared.
Karasik, Boris S.; Pereverzev, Sergey V.; Soibel, Alexander; Santavicca, Daniel F.; Prober, Daniel E.; Olaya, David; Gershenson, Michael E.
Superconducting magnetic energy storage (SMES) program. Progress report, January 1-December 31, 1980
Work is reported on the development of two superconducting magnetic energy storage (SMES) units. One is a 30-MJ unit for use by the Bonneville Power Administration (BPA) to stabilize power oscillations on their Pacific AC Intertie, and the second is a 1- to 10-GWh unit for use as a diurnal load leveling device. Emphasis has been on the stabilizing system. The manufacturing phase of the 30-MJ superconducting coil was initiated and the coil fabrication has advanced rapidly. The two converter power transformers were manufactured, successfully factory tested, and shipped. One transformer reached the Tacoma Substation in good condition; the other was dropped enroute and has been returned to the factory for rebuilding. Insulation of the 30-MJ coil has been examined for high voltage effects apt to be caused by transients such as inductive voltage spikes from the protective dump circuit. The stabilizing system converter and protective energy dump system were completed, factory tested, and delivered.
Energy Recovery LINAC (ERL) and LINAC-driven FEL proposals and developments are now widespread around the world. Superconducting RF (SRF) cavity advances made over the last 10 years for TESLA\\/TTF at 1.3 GHz, in reliably achieving accelerating gradients >20 MV\\/m, suggest their suitability for these ERL and FEL accelerators. Typically however, photon fluxes are maximised from the associated insertion devices when
P. A. McIntosh; C. D. Beard; D. M. Dykes; B. Todd; S. Belomestnykh; M. Liepe; V. Medjidzade; H. Padamsee; J. Sears; V. D. Shemelin; D. Proch; A. Buechner; P. Michel; J. Teichert; T. Kimura; T. I. Smith; J. Byrd; J. N. Corlett; D. Li
Energy calibration of superconducting transition edge sensors for x-ray detection using pulse analysis
Transition edge sensors (TESs) have been developed to be used as high-resolution x-ray detectors. They show excellent energy resolution and can be used in many applications. TESs are a special kind of calorimeters that can determine small temperature changes after x-ray absorption. Such a temperature change causes a strong resistance change (superconducting to normal-conducting phase transition) that can be measured.
C. Hollerith; B. Simmnacher; R. Weiland; F. V. Feilitzsch; C. Isaila; J. Jochum; W. Potzel; J. Hoehne; K. Phelan; D. Wernicke; T. May
Robust damping controller design in power systems with superconducting magnetic energy storage devices
The decentralized design of low-order robust damping controllers is presented based on a weighted and normalized eigenvalue-distance minimization method (WNEDM) employing several superconducting magnetic energy storage (SMES) devices. These controllers are aimed at enhancing the damping of multiple inter-area modes in a large power system. This paper describes a comprehensive and systematic way of designing these controllers. Nonlinear simulations further
Bikash C. Pal; Alun H. Coonick; D. C. Macdonald
Phonon self-energy effects due to superconductivity: A real-axis formulation
The self-energy of {bold q}={bold 0} phonons is calculated in both the superconducting and normal states, with use of a real-axis formulation, valid for arbitrary temperature, impurity scattering rate, and electron-phonon coupling strength. The calculations are performed within the Eliashberg framework. We qualitatively confirm much of the previous work done using Pade approximants. Besides providing quantitative corrections, we also predict an observable effect with low-frequency phonons.
Marsiglio, F. (Theoretical Physics Branch, AECL Research, Chalk River Laboratories, Chalk River, Ontario, K0J1J0 (Canada)); Akis, R.; Carbotte, J.P. (Department of Physics, McMaster University, Hamilton, Ontario, L8S4M1 (Canada))
Pressure coefficient of the PbTe metastable CsCl-type-phase energy gap
The transmittance and reflectance spectra of PbTe films grown on different substrates (KBr, KCl, BaF2) by the nonequilibrium growth technique of laser-assisted deposition are investigated. The films represent two-layer structures: the sublayer, adjacent to the substrate, consists of the high-pressure metastable CeCl-type phase while the upper sublayer is of the stable fcc phase. As the metastable-CeCl-type-phase lattice volume depends on the substrate nature, we investigate PbTe films with CsCl-type phase corresponding to different pressures. The optical energy gaps in the various films are determined from the maxima in the refractive index dispersions, calculated from the transmittance and reflectance spectra. Thus, the energy-gap pressure coefficient in the PbTe CsCl-type metastable phase is obtained.
Baleva, M.; Mateeva, E.
Energy-Gap Opening in a Bi(110) Nanoribbon Induced by Edge Reconstruction
Scanning tunnelling microscopy and spectroscopy experiments complemented by first-principles calculations have been conducted to study the electronic structure of 4 monolayer Bi(110) nanoribbons on epitaxial graphene on silicon carbide [4H-SiC(0001)]. In contrast with the semimetal property of elemental bismuth, an energy gap of 0.4 eV is measured at the centre of the Bi(110) nanoribbons. Edge reconstructions, which can facilitate the edge strain energy release, are found to be responsible for the band gap opening. The calculated density of states around the Fermi level are decreased quickly to zero from the terrace edge to the middle of a Bi(110) nanoribbon potentially signifying a spatial metal-to-semiconductor transition. This study opens new avenues for room-temperature bismuth nanoribbon-based electronic devices.
Sun, Jia-Tao; Huang, Han; Wong, Swee Liang; Gao, H.-J.; Feng, Yuan Ping; Wee, Andrew Thye Shen
Low-energy bound states at interfaces between superconducting and block antiferromagnetic regions in KxFe2-ySe2
The high-Tc alkali doped iron selenide superconductors KxFe2-ySe2 have been recently shown to be intrinsically phase separated into Fe vacancy ordered block antiferromagnetic regions and superconducting regions at low temperatures. In this work, we use a microscopic five orbital Hubbard model to obtain the electronic low-energy states near the interfaces between block antiferromagnets and superconductors. It is found that abundant low-energy in-gap bound states exist near such interfaces irrespective of whether the superconductor has d- or s-wave pairing symmetry. By contrast, it is shown how scattering from (110) boundaries can provide a natural means to distinguish between these two leading pairing instabilities of the KxFe2-ySe2 materials.
Mukherjee, S.; Gastiasoro, M. N.; Hirschfeld, P. J.; Andersen, B. M.
Destruction of superconductivity in quench-condensed two-dimensional films
We have performed systematic tunneling measurements on two-dimensional quench-condensed films of Sn and Pb to investigate the destruction of superconductivity by localization effects. With increasing sheet resistance of the films, the energy gaps and T/sub c/'s decrease only slightly, but the gap edges broaden until the width becomes comparable to the gap. Associated with this broadening are low-temperature finite-resistance tails in the resistive transitions.
White, A.E.; Dynes, R.C.; Garno, J.P.
Electronic energy gap of molecular hydrogen from electrical conductivity measurements at high shock pressures
Electrical conductivities were measured for liquid D2 and H2 shock compressed to pressures of 10-20 GPa (100-200 kbar), molar volumes near 8 cu cm/mol, and calculated temperatures of 2900-4600 K. The semiconducting energy gap derived from the conductivities is 12 eV, in good agreement with recent quasi-particle calculations and with oscillator frequencies measured in diamond-anvil cells.
Nellis, W. J.; Mitchell, A. C.; Mccandless, P. C.; Erskine, D. J.; Weir, S. T.
Energy gaps, magnetism, and electric-field effects in bilayer graphene nanoribbons
Using a first principles density functional electronic structure method, we\\u000astudy the energy gaps and magnetism in bilayer graphene nanoribbons as a\\u000afunction of the ribbon width and the strength of an external electric field\\u000abetween the layers. We assume AB (Bernal) stacking and consider both armchair\\u000aand zigzag edges and two edge alignments distinguished by a 60$^o$ rotation of
Bhagawan Sahu; Hongki Min; Allan. H. MacDonald; Sanjay K. Banerjee
Linear properties of finite photonic band gap structures: Group velocity, energy velocity, and effective dispersion relations
A re-evaluation of the notions of group (Vg) and energy (Ve) velocities in finite photonic band gap structures leads us to conclude that the two velocities are related by Ve=|t|2Vg and that Ve=Vg only at each peak of transmission (|t|2=1). This result impacts our understanding of the effective dispersion properties of layered materials, and can be used to better understand
Giuseppe DÆAguanno; Redstone Arsenal
Increasing the ? = 5/2 gap energy: an analysis of MBE growth parameters
The fractional quantized Hall state at the filling factor ? = 5/2 is of special interest due to its possible application for quantum computing. Here we report on the optimization of growth parameters that allowed us to produce two-dimensional electron gases (2DEGs) with a 5/2 gap energy up to 135 mK. We concentrated on optimizing the molecular beam epitaxy (MBE) growth to provide high 5/2 gap energies in æas-grownÆ samples, without the need to enhance the 2DEGs properties by illumination or gating techniques. Our findings allow us to analyse the impact of doping in narrow quantum wells with respect to conventional DX-doping in AlxGa1-xAs. The impact of the setback distance between doping layer and 2DEG was investigated as well. Additionally, we found a considerable increase in gap energy by reducing the amount of background impurities. To this end growth techniques like temperature reductions for substrate and effusion cells and the reduction of the Al mole fraction in the 2DEG region were applied.
Reichl, C.; Chen, J.; Baer, S.; R÷ssler, C.; Ihn, T.; Ensslin, K.; Dietsche, W.; Wegscheider, W.
Low Energy Particle Detector Using a Superconducting Transition Edge Sensor
Precise measurement of neutron beta decay tests predictions of the Standard Model of electroweak interaction. The coefficient a of the antineutrino\\/electron angular correlation is determined by measuring the energy spectrum of the recoil protons generated in the neutron beta decay. A proton spectrometer required for this measurement demands high detection efficiency, high energy resolution and a large detection area. We
Masashi Ohno; Hiromi Sato; Kenji Mishima; Tokihiro Ikeda; Hirohiko M. Shimizu
Distinct pseudogap and superconducting state quasiparticle relaxation dynamics in near-optimally doped SmFeAsO0.8F0.2 single crystals
We use femtosecond spectroscopy to investigate the quasiparticle relaxation and low-energy electronic structure in a near-optimally doped pnictide superconductor with T_c=49.5 K. Multiple relaxation processes are evident, with distinct superconducting state quasiparticle (QP) recombination dynamics exhibiting a T-dependent superconducting (SC) gap, and a clear \\
T. Mertelj; V. V. Kabanov; C. Gadermaier; J. Karpinski; D. Mihailovic
Large gap magnetic suspension system
The design of a large gap magnetic suspension system is discussed. Some of the topics covered include: the system configuration, permanent magnet material, levitation magnet system, superconducting magnets, resistive magnets, superconducting levitation coils, resistive levitation coils, levitation magnet system, and the nitrogen cooled magnet system.
Abdelsalam, Moustafa K.; Eyssa, Y. M.
Energy gap of tight-binding electrons on generalized honeycomb lattice
So as to clearly understand the energy band gap of graphene, we study the energy band of tight-binding electrons on a honeycomb lattice with on-site potentials ?A and ?B on sublattices A and B, nearest-neighbor transfer integrals ta, tb and tc, and next-nearest-neighbor transfer integrals t2a, t2b, t2c, t2d, t2e and t2f, where t2a, t2b and t2C are transfer integrals between sublattice A, and t2d, t2e and t2f are transfer integrals between sublattice B.
Kishigi, Keita; Takeda, Ryuichi; Hasegawa, Yasumasa
Vanishing electronic energy loss of very slow light ions in insulators with large band gaps.
Electronic energy loss of light ions in nanometer films of materials with large band gaps has been studied for very low velocities. For LiF, a threshold velocity is observed at 0.1 a.u. (250 eV/u), below which the ions move without transferring energy to the electronic system. For KCl, a lower (extrapolated) threshold velocity is found, identical for H and He ions. For SiO2, no clear velocity threshold is observed for He particles. For protons and deuterons, electronic stopping is found to perfectly fulfill velocity scaling, as expected for binary ion-electron interaction. PMID:19792368
Markin, S N; Primetzhofer, D; Bauer, P
Vanishing Electronic Energy Loss of Very Slow Light Ions in Insulators with Large Band Gaps
Electronic energy loss of light ions in nanometer films of materials with large band gaps has been studied for very low velocities. For LiF, a threshold velocity is observed at 0.1 a.u. (250 eV/u), below which the ions move without transferring energy to the electronic system. For KCl, a lower (extrapolated) threshold velocity is found, identical for H and He ions. For SiO{sub 2}, no clear velocity threshold is observed for He particles. For protons and deuterons, electronic stopping is found to perfectly fulfill velocity scaling, as expected for binary ion-electron interaction.
Markin, S. N.; Primetzhofer, D.; Bauer, P. [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet Linz, A-4040 Linz (Austria)
Destruction of superconductivity in current carrying NbTi fibers by strain energy
Individual thin fibers of NbTi (46.5 wt % Ti) have been driven from the superconducting to the normal state by tensile force while immersed in liquid helium and carrying subcritical currents. The additional force for successive excursions from the superconducting to the normal state has been measured and found to saturate. This ''mechanical training'' can be reduced to the starting state for a fiber while at zero load by exceeding the critical current. Estimates are made of the mechanical energy to initiate quenching and since the tensile machine is ''hard'' estimates have also been made of the rise in temperature while subjected to short bursts of current greater than critical. There would appear to be structural changes which are stress level dependent and of a ''shape memory'' nature.
Wright, L.S.; Hutchison, T.S.; Wiederick, H.D.
Preparation of Nb3Al by high-energy ball milling and superconductivity
The A15 phase superconductor Nb3Al has been considered as an alternative to Nb3Sn for high field and large scale applications. However, to prepare a stoichiometric Nb3Al with fine grain structures is very difficult. High-energy ball milling is a solid state powder processing technique and is a very useful for preparing Nb-Al alloys (Nb3Al). The effects of ball milling time and annealing temperature on the formation of Nb3Al superconducting phase have been studied. Pure Nb and Al powders with stoichiometric ratio of Nb3Al were mixed and milled, and the charging and milling were performed in an inert atmosphere. Phase formation and structural evolution during high-energy ball milling have been examined by X-ray diffraction. Al disappeared and Nb peaks broadened after about one hour of milling. With increasing milling time, the peaks of Nb became considerably broader and intensities decreased, the Nb-Al solid solution phase was extensive when milled about 3 hours. In order to obtain Nb3Al superconducting phase, a subsequent anneal was required. We have annealed the as-milled powders at 800-900░C for different times to prepared Nb3Al superconducting alloy. The results indicated that Nb3Al with small amount of impurity phase can be obtained on annealing the Nb-Al solid solution phase and the superconducting transition temperature was about 15K, but it is difficult to obtain a homogeneous Nb3Al phase by annealing the amorphous powder.
Chen, Yongliang; Liu, Zhao; Li, Pingyuan; Zhang, Xiaolan; Yang, Suhua; Yang, Dawei; Du, Lupeng; Cui, Yajing; Pan, Xifeng; Yan, Guo; Zhao, Yong
Energy transfer experiments between 3 MJ and 4 MJ pulsed superconducting magnets
The pulsed power supply system for a 3 MJ pulsed superconducting magnets by using an energy storage magnet and a transfer circuit was constructed. It is composed of both 3 MJ and 4 MJ pulsed superconducting magnets (named PSM-3 and SMES-4, respectively) and the energy transfer apparatus which consists of the chopper circuit with a capacity of about 5000 kW. The reversible energy transfer experiments between SMES-4 and PSM-3 were carried out, and with the SMES-4 charged up to 4.24 MJ initial energy, the PSM-3 was successfully charged up to 2.45 MJ (4950 A, B /SUB m/ : 5.94 T) in 1.5 seconds and also up to 2.9 MJ (5400 A, B /SUB m/ : 6.48 T) in 3.0 seconds. The maximum delivery power was about 3270 kW. The energy transfer efficiency in one way transfer was about 93%, and the current ripple was less than 0.01% of a rating current. The two pulsed magnets showed very stable performances during the energy transfers.
Onishi, T.; Ichihara, T.; Komuro, K.; Koyama, K.; Tateishi, H.; Tukeda, M.
Glassy low-energy spin fluctuations and anisotropy gap in La1.88Sr0.12CuO4
We present high-resolution triple-axis neutron scattering studies of the high-temperature superconductor La1.88Sr0.12CuO4 (Tc=27 K). The temperature dependence of the low-energy incommensurate magnetic fluctuations reveals distinctly glassy features. The glassiness is confirmed by the difference between the ordering temperature TN?Tc inferred from elastic neutron scattering and the freezing temperature Tf?11 K obtained from muon spin rotation studies. The magnetic field independence of the observed excitation spectrum as well as the observation of a partial suppression of magnetic spectral weight below 0.75 meV for temperatures smaller than Tf, indicate that the stripe frozen state is capable of supporting a spin anisotropy gap, of a magnitude similar to that observed in the spin and charge stripe-ordered ground state of La1.875Ba0.125CuO4. The difference between TN and Tf implies that the significant enhancement in a magnetic field of nominally elastic incommensurate scattering is caused by strictly inelastic scatteringŚat least in the temperature range between Tf and TcŚwhich is not resolved in the present experiment. Combining the results obtained from our study of La1.88Sr0.12CuO4 with a critical reappraisal of published neutron scattering work on samples with chemical composition close to p=0.12, where local probes indicate a sharp maximum in Tf(p), we arrive at the view that the low-energy fluctuations are strongly dependent on composition in this regime, with anisotropy gaps dominating only sufficiently close to p=0.12 and superconducting spin gaps dominating elsewhere.
R°mer, A. T.; Chang, J.; Christensen, N. B.; Andersen, B. M.; Lefmann, K.; Mõhler, L.; Gavilano, J.; Gilardi, R.; Niedermayer, Ch.; R°nnow, H. M.; Schneidewind, A.; Link, P.; Oda, M.; Ido, M.; Momono, N.; Mesot, J.
Superconductivity applications for infrared and microwave devices; Proceedings of the Meeting, Orlando, FL, Apr. 19, 20, 1990
Various papers on superconductivity applications for IR and microwave devices are presented. The individual topics addressed include: pulsed laser deposition of Tl-Ca-Ba-Cu-O films, patterning of high-Tc superconducting thin films on Si substrates, IR spectra and the energy gap in thin film YBa2Cu3O(7-delta), high-temperature superconducting thin film microwave circuits, novel filter implementation utilizing HTS materials, high-temperature superconductor antenna investigations, high-Tc superconducting IR detectors, high-Tc superconducting IR detectors from Y-Ba-Cu-O thin films, Y-Ba-Cu0-O thin films as high-speed IR detectors, fabrication of a high-Tc superconducting bolometer, transition-edge microbolometer, photoresponse of YBa2Cu3O(7-delta) granular and epitaxial superconducting thin films, fast IR response of YBCO thin films, kinetic inductance effects in high-Tc microstrip circuits at microwave frequencies.
Bhasin, K.B.; Heinen, V.O.; (NASA, Lewis Research Center, Cleveland, OH)
Ground state energy and scaling behaviour of spin gap in the XXZ spin-12 antiferromagnetic chain in longitudinal staggered field
The ground state energy and the spin gap of a spin-12 Heisenberg antiferromagnetic XXZ chain in the presence of longitudinal staggered field (hz) have been estimated by using Jordan¢Wigner representation, exact diagonalization and perturbative analysis. All those quantities have been obtained for a region of anisotropic parameter (?) defined by 0???1. For ?=0, the exact value of ground state energy is found for finite values of hz. The spin gap is found to develop as soon as the staggered field is switched on. The magnitude of spin gap is compared with the field induced gap measured in magnetic compounds CuBenzoate and Yb4As3 when ?=1. The dependence of spin gap on both ? and hz has been found which gives rise to scaling laws associated with hz. Scaling exponents obtained in two different cases show excellent agreements with the previously determined values. The variation of scaling exponents with ? can be fitted with a regular function.
Paul, Susobhan; Ghosh, Asim Kumar
Superconducting High Energy Resolution Gamma-ray Spectrometers
We have demonstrated that a bulk absorber coupled to a TES can serve as a good gamma-ray spectrometer. Our measured energy resolution of 70 eV at 60 keV is among the best measurements in this field. We have also shown excellent agreement between the noise predictions and measured noise. Despite this good result, we noted that our detector design has shortcomings with a low count rate and vulnerabilities with the linearity of energy response. We addressed these issues by implementation of an active negative feedback bias. We demonstrated the effects of active bias such as additional pulse shortening, reduction of TES change in temperature during a pulse, and linearization of energy response at low energy. Linearization at higher energy is possible with optimized heat capacities and thermal conductivities of the microcalorimeter. However, the current fabrication process has low control and repeatability over the thermal properties. Thus, optimization of the detector performance is difficult until the fabrication process is improved. Currently, several efforts are underway to better control the fabrication of our gamma-ray spectrometers. We are developing a full-wafer process to produce TES films. We are investigating the thermal conductivity and surface roughness of thicker SiN membranes. We are exploring alternative methods to couple the absorber to the TES film for reproducibility. We are also optimizing the thermal conductivities within the detector to minimize two-element phonon noise. We are experimenting with different absorber materials to optimize absorption efficiency and heat capacity. We are also working on minimizing Johnson noise from the E S shunt and SQUID amplifier noise. We have shown that our performance, noise, and active bias models agree very well with measured data from several microcalorimeters. Once the fabrication improvements have been implemented, we have no doubt that our gamma-ray spectrometer will achieve even more spectacular results.
Chow, D T
Distinct Pseudogap and Quasiparticle Relaxation Dynamics in the Superconducting State of Nearly Optimally Doped SmFeAsO0.8F0.2 Single Crystals
We use femtosecond spectroscopy to investigate the quasiparticle relaxation and low-energy electronic structure in a nearly optimally doped pnictide superconductor with Tc=49.5K. Multiple relaxation processes are evident, with distinct superconducting state quasiparticle recombination dynamics exhibiting a T-dependent superconducting gap, and a clear ``pseudogaplike'' feature with an onset above 180 K indicating the existence of a temperature-independent gap of magnitude DeltaPG=61▒9meV
T. Mertelj; V. V. Kabanov; C. Gadermaier; N. D. Zhigadlo; S. Katrych; J. Karpinski; D. Mihailovic
Superconducting Polarons and Bipolarons
The seminal work by Bardeen, Cooper and Schrieffer (BCS) extended further by Eliashberg to the intermediate coupling regime solved one of the major scientific problems of Condensed Matter Physics in the last century. The BCS theory provides qualitative and in many cases quantitative descriptions of low-temperature superconducting metals and their alloys, and some novel high-temperature superconductors like magnesium diboride. The theory has been extended by us to the strong-coupling regime where carriers are small lattice polarons and bipolarons. Here I review the multi-polaron strong-coupling theory of superconductivity. Attractive electron correlations, prerequisite to any superconductivity, are caused by an almost unretarded electron-phonon (e-ph) interaction sufficient to overcome the direct Coulomb repulsion in this regime. Low energy physics is that of small polarons and bipolarons, which are real-space electron (hole) pairs dressed by phonons. They are itinerant quasiparticles existing in the Bloch states attemperatures below the characteristic phonon frequency. Since there is almost no retardation (i.e. no Tolmachev-Morel-Anderson logarithm) reducing the Coulomb repulsion, e-ph interactions should be relatively strong to overcome the direct Coulomb repulsion, so carriers mustbe polaronic to form pairs in novel superconductors. I identify the long-range Fr÷hlich electron-phonon interaction as the most essential for pairing in superconducting cuprates. A number of key observations have been predicted or explained with polarons and bipolarons including unusual isotope effects and upper critical fields, normal state (pseudo)gaps and kinetic properties, normal state diamagnetism, and giant proximity effects. These and many other observations provide strong evidence for a novel state of electronic matter in layered cuprates, which is a charged Bose-liquid of small mobile bipolarons.
Alexandrov, A. S.
Josephson effect and nonequilibrium superconductivity in superconducting tunnel structures
Nonequilibrium superconductivity induced by tunnel current injection of quasiparticles is studied. It is found that an instability in the form of a negative voltage jump in the oscillator current-voltage characteristic (CVC), which leads to an inhomogeneous state, as well as the spatial structure of the inhomogeneous state are very sensitive to low magnetic fields. The shape of the CVC of low-resistance tunnel junctions for bias voltages V ~ 2?/e depends strongly on the junction dimensions and barrier transparency. These results are interpreted in terms of Josephson vortices (fluxons) in a tunnel oscillator. Studies of the nonequilibrium phenomena, with the Josephson properties of low-resistance tunnel structures taken into account, reveal a number of new effects, such as nonequilibrium suppression of the energy gap at bias voltages V < 2?/e, the possible existence of an entire series of instabilities of the nonequilibrium superconducting state during tunnel injection, and inhomogeneity in the tunnel injector effect.
Rudenko, E. M.
Strain energy minimization in SSC (Superconducting Super Collider) magnet winding
Differential geometry provides a natural family of coordinate systems, the Frenet frame, in which to specify the geometric properties of magnet winding. By a modification of the Euler-Bernoulli thin rod model, the strain energy is defined with respect to this frame. Then it is minimized by a direct method from the calculus of variations. The mathematics, its implementation in a computer program, and some analysis of an SSC dipole by the program will be described. 16 refs.
Cook, J.M.
Disorder effects on superconducting tendencies in the checkerboard Hubbard model
The question of whether spatially inhomogeneous hopping in the two dimensional Hubbard model can lead to enhancement of superconductivity has been tackled by a number of authors in the context of the checkerboard Hubbard model (CHM). We address the effects of disorder on superconducting properties of the CHM by using exact diagonalization calculations for both potential and hopping disorder. We characterize the superconducting tendencies of the model by focusing on the pair-binding energy, the spin gap, and d-wave pairing order parameter. We find that superconducting tendencies, particularly the pair-binding energy, are more robust to disorder when there is inhomogeneous hopping than for the uniform Hubbard model. We also study all possible staggered potentials for an eight-site CHM cluster and relate the behavior of these configurations to the disordered system.
Smith, Peter M.; Kennett, Malcolm P.
The Energy Band Gap of AlxGa1-xN
Combining experimental measurements with an analysis of sample strain, we have determined the ōunstrainedö energy band gap, Eg, of AlxGa1-xN for 0 ? x ? 1. Care was taken to grow films with narrow (00.2) and (10.2) X-ray diffraction rocking curve widths, to insure low residual strain in the samples. This is significant because, even for our high quality AlxGa1-xN thin films, residual strain shifts the fitted band gap bowing parameter significantly. For AlxGa1-xN random alloys on GaN films deposited on sapphire, the strain-corrected band gap dependence on alloy composition is fit well by a bowing parameter of b = 0.70 ▒ 0.05. In contrast, AlxGa1-xN films deposited directly on sapphire had much higher X-ray line-widths and their EgÆs are not fit well by one value of the bowing parameter. This suggests that material quality may be a significant reason for the large range of bowing parameters reported in the literature.
Paduano, Qing S.; Weyburne, David W.; Bouthillette, Lionel O.; Wang, Shen-Qi; Alexander, Michael N.
Neutron Scattering Studies On Stoner Gap In The Superconducting Ferromagnet UGe2 By Using A Small Piston-Cylinder-Type Clamp Cell
The design and fundamental properties of a small copper-beryllium (CuBe) based piston-cylinder-type clamp cell for low-temperature (LT) neutron diffraction (ND) measurements are reported. The results obtained for the superconducting ferromagnet UGe2 showed that the perfectly polarized ferromagnetic state is realized below Px.
N. Aso; Y. Uwatoko; T. Fujiwara; G. Motoyama; S. Ban; Y. Homma; Y. Shiokawa; K. Hirota; N. K. Sato
Aso, N.; Uwatoko, Y.; Fujiwara, T.; Motoyama, G.; Ban, S.; Homma, Y.; Shiokawa, Y.; Hirota, K.; Sato, N. K.
ORNL Superconducting Technology Program for Electric Energy Systems. Annual report for FY 1992
The Oak Ridge National Laboratory (ORNL) Superconducting Technology Program is conducted as part of a national effort by the US Department of Energy`s (DOE`s) Office of Conservation and Renewable Energy to develop the technology base needed by US industry for commercial development of electric power applications of high-temperature superconductivity. The two major elements of this program are wire development and systems development. This document describes the major research and development activities for this program together with related accomplishments. The technical progress reported was summarized from information prepared for the FY 1992 Peer Review of Projects, conducted by DOE`s Office of Program Analysis, Office of Energy Research. This ORNL program is highly leveraged by the staff and other resources of US industry and universities. Interlaboratory teams are also in place on a number of industry-driven projects. Patent disclosures, working group meetings, staff exchanges, and joint publications and presentations ensure that there is technology transfer to US industry. Working together, the collaborative teams are making tremendous progress in solving the scientific and technical issues necessary for the commercialization of long lengths of practical high-temperature superconductor wire and wire products.
Hawsey, R.A. [comp.
Bound state energy of a Coulomb impurity in gapped bilayer graphene
Application of a perpendicular electric field induces a band gap in bilayer graphene, and it also creates a "Mexican hat" structure in the dispersion relation. This structure has unusual implications for the hydrogen-like bound state of an electron to a Coulomb impurity. We calculate the ground state energy of this hydrogen-like state as a function of the applied interlayer voltage and the effective fine structure constant. Unlike in the conventional hydrogen atom, the resulting wave function has many nodes even in the ground state. Further, the electron state undergoes "atomic collapse" into the Dirac continuum both at small and large voltage.
Skinner, Brian; Shklovskii, B. I.; Voloshin, M. B.
Superconducting cables: long-distance energy transmission. January 1973-February 1988 (Citations from the NTIS data base). Report for January 1973-February 1988
This bibliography contains citations concerning the design, development, and evaluation of superconducting cables and power-transmission lines for long-distance energy transmission. Topics include methods of cryogenic refrigeration and electrical insulation, fabrication and development of niobium-alloy conductors, energy-loss analysis, and dielectric-design techniques for superconducting power-transmission systems. Government research project reports on superconducting technology for electric-power transmission and distribution are included. (Contains 129 citations fully indexed and including a title list.)
Superconducting magnetic energy storage scaled prototype for the Los Alamos utility
A complete analysis of the combined Department of Energy (DOE) - Los Alamos National Laboratory, Los Alamos County electric utility was performed to determine the differential cost saving for diurnal load leveling by displacing one of several energy sources with energy stored from the Western Area Power Administration in a superconducting magnetic energy storage (SMES) unit. The base case for the model for comparison is the best concept considered to date - the planned DOE/County power pool composed of a number of sources. Advantageous displacement costs appear available based upon a SMES unit rated at 144 MWh and 20 MW. The prospect of a prototype SMES plant to demonstrate the technology seems to be favorable.
Rogers, J.D.; Kiburz, M.E.
Superconducting magnetic energy storage. (Latest citations from the INSPEC database). Published Search
The bibliography contains citations concerning research, development, and assessment of superconducting magnetic energy storage (SMES) technology. References discuss the design and performance of toroidal and solenoid type SMES systems for military, space mission, and electric utility applications. Topics include active and reactive power control, power system stability and diagnosis, power supply quality, uninterruptible power supplies, and SMES systems for critical industrial and military uses. Cost analysis and optimization, marketing, and environmental issues are reviewed. (Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)
30-MJ superconducting magnetic energy storage for BPA transmission-line stabilizer
The Bonneville Power Administration operates the transmission system that joins the Pacific Northwest and southern California. A 30 MJ (8.4 kWh) superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter can provide system damping for low frequency oscillations. The unit is scheduled to operate in late 1982. Progress to date is described. The coil is complete. All major components of the electrical and cryogenic systems have been received and testing has begun. Computer control hardware is in place and software development is proceeding. Support system components and dewar lid are being fabricated and foundation design is complete. A contract for dewar fabrication is being negotiated.
Schermer, R.I.
30 MJ superconducting magnetic energy storage stabilizing coil. Final report for construction
This report covers Phase II, Fabrication and Delivery of the 30 MJ Superconducting Magnetic Energy Storage Stabilizing Coil. A history of the manufacturing and assembly phase of the magnet is presented. Major problems and solutions are summarized, and illustrations of the major operations are provided. The Quality Assurance program is described with a listing of all nonconformance reports. Design documentation is provided, including a Design Document Index, monthly progress reports, and a list of papers given on the project. Appendices to the report contain copies of released and revised design calculations, test reports, assembly procedure, and nonconformance reports and engineering dispositions.
Production techniques for the Superconducting Super Collider Low Energy Booster quadrupole magnet
The manufacturing techniques used for a prototype quadrupole magnet, developed at Lawrence Berkeley Laboratory (LBL) for the Superconducting Super Collider (SSC) Low Energy Booster (LEB), are described. The SSC LEB Ring employs 96 dipoles and 90 quadrupoles connected in series to form the magnetic lattice, requiring the use of a 21.9 mm x 23.0 mm hollow conductor for the quadrupoles. Due to the large conductor size and small bend radii required, development of special fixtures was necessary. A unique coil-forming method with close attention paid to tooling design and special assembly procedures was required to manufacture this prototype to stringent specifications.
Morrison, M.E.; Behrsing, G.U.; Fulton, R.L. [Lawrence Berkeley Lab., CA (United States)] [Lawrence Berkeley Lab., CA (United States)
Development of large high current density superconducting solenoid magnets for use in high energy physics experiments. [Thesis
The development of a unique type of large superconducting solenoid magnet, characterized by very high current density windings and a two-phase helium tubular cooling system is described. The development of the magnet's conceptual design and the construction of two test solenoids are described. The successful test of the superconducting coil and its tubular cooling refrigeration system is presented. The safety, environmental and economic impacts of the test program on future developments in high energy physics are shown. Large solid angle particle detectors for colliding beam physics will analyze both charged and neutral particles. In many cases, these detectors will require neutral particles, such as gamma rays, to pass through the magnet coil with minimum interaction. The magnet coils must be as thin as possible. The use of superconducting windings allows one to minimize radiation thickness, while at the same time maximizing charged particle momentum resolution and saving substantial quantities of electrical energy. The results of the experimental measurements show that large high current density solenoid magnets can be made to operate at high stored energies. The superconducting magnet development described has a positive safety and environmental impact. The use of large high current density thin superconducting solenoids has been proposed in two high energy physics experiments to be conducted at the Stanford Linear Accelerator Center and Cornell University as a result of the successful experiments described.
Green, M.A.
Electron tunneling into superconductive lead-indium alloys subjected to hydrostatic pressure
Results are presented for electron tunneling studies of superconducting lead-indium alloys (Pb0.88In0.12 and Pb0.64In0.36) as a function of pressure. The pressure dependence of the energy gap ?0, the reduced energy gap 2?0\\/kTc, and the electron-phonon coupling constant ? show that under pressure the alloys move toward weaker coupling. The numerical agreement with estimates from the strong coupling theory is excellent.
P. W. Wright; J. P. Franck
Predictions of anisotropic superconductivity in UIr/sub 3/ and UPt/sub 3/
Anisotropic singlet state superconductivity is predicted for UIr/sub 3/ (an itinerant non-heavy fermion intermetallic) as was done earlier for UPt/sub 3/ (perhaps the prototype heavy fermion system). In both, this arises from strong Uf-Xd hybridization which yields a highly anisotropic Fermi surface (now confirmed by dHvA experiments of Taillefer et al. on UPt/sub 3/), electron - phonon interaction, and superconducting energy gap.
Oguchi, T.; Freeman, A.J.; Crabtree, G.W.
Closing data gaps for LCA of food products: estimating the energy demand of food processing.
Food is one of the most energy and CO2-intensive consumer goods. While environmental data on primary agricultural products are increasingly becoming available, there are large data gaps concerning food processing. Bridging these gaps is important; for example, the food industry can use such data to optimize processes from an environmental perspective, and retailers may use this information for purchasing decisions. Producers and retailers can then market sustainable products and deliver the information demanded by governments and consumers. Finally, consumers are increasingly interested in the environmental information of foods in order to lower their consumption impacts. This study provides estimation tools for the energy demand of a representative set of food process unit operations such as dehydration, evaporation, or pasteurization. These operations are used to manufacture a variety of foods and can be combined, according to the product recipe, to quantify the heat and electricity demand during processing. In combination with inventory data on the production of the primary ingredients, this toolbox will be a basis to perform life cycle assessment studies of a large number of processed food products and to provide decision support to the stakeholders. Furthermore, a case study is performed to illustrate the application of the tools. PMID:24344613
Sanjußn, Neus; Stoessel, Franziska; Hellweg, Stefanie
Band Edge Energies and Band Gaps of Quaternary GaInAsSb Alloys
Quaternary alloys without a common atom such as (Ga,In)-(As,Sb) pose a difficult combinatorially design problem in that there are many different atomic configurations even when the system is constrained to be lattice-matched on a substrate. Using an atomistic pseudopotential approach we have calculated the band edge energies of this quaternary random alloys as a function of Ga/In (x) and As/Sb (y) compositions assuming lattice-matching to either GaSb or InAs. The alloy is represented by a large supercell with random atomic occupations and atomic positions relaxed via the atomistic VFF functional. We find upwards bowing for both the conduction and valence band edge energies. On GaSb, the transition from staggered to broken-gap lineup is found to occur at x = 0.81 and y = 0.92, while on InAs it occurs at x = 0.59 and y = 0.62. We show that at the usual growth temperatures this quaternary alloy is not random but tends to exhibit an increased number of Ga-Sb and In-As bonds and a reduced number of In-Sb and Ga-As bonds. This effect brings the calculated band gaps in better agreement with experimental data. T. Magri, A. Zunger, H. Kroemer, JAP 98, 043701 (2005)
Magri, Rita; Zunger, Alex; Kroemer, Herbert
Group velocity, energy velocity, and superluminal propagation in finite photonic band-gap structures
We have analyzed the notions of group velocity Vg and energy velocity VE for light pulses propagating inside one-dimensional photonic band gap structures of finite length. We find that the two velocities are related through the transmission coefficient t as VE=\\|t\\|2Vg. It follows that VE=Vg only when the transmittance is unity (\\|t\\|2=1). This is due to the effective dispersive properties of finite layered structures, and it allows us to better understand a wide range of phenomena, such as superluminal pulse propagation. In fact, placing the requirement that the energy velocity should remain subluminal leads directly to the condition Vg<=c/\\|t\\|2. This condition places a large upper limit on the allowed group velocity of the tunneling pulse at frequencies of vanishingly small transmission.
D'aguanno, G.; Centini, M.; Scalora, M.; Sibilia, C.; Bloemer, M. J.; Bowden, C. M.; Haus, J. W.; Bertolotti, M.
FAST TRACK COMMUNICATION: Ion energy and angular distributions into the wafer-focus ring gap in capacitively coupled discharges
The termination of the edge of wafers in reactive ion etching reactors is important for obtaining uniform fluxes of reactants across the substrate. Structures such as focus rings (FRs) are often used to improve the uniformity of fluxes. There is a gap of hundreds of micrometres to a few mm between the edge of the wafer and the FR for mechanical clearance. Plasma penetration into the gap can produce particle forming films and erosion of consumable parts. In this paper, we discuss results from a computational investigation of ion energy and angular distributions incident into the wafer-focus ring gap. The geometry and electrical properties of the FR can skew the angle and limit the extent of energies of ions penetrating into the gap.
Babaeva, Natalia Y.; Kushner, Mark J.
Tunable Coupling in Circuit Quantum Electrodynamics Using a Superconducting Charge Qubit with a V-Shaped Energy Level Diagram
We introduce a new type of superconducting charge qubit that has a V-shaped energy spectrum and uses quantum interference to provide independently tunable qubit energy and coherent coupling to a superconducting cavity. Dynamic access to the strong coupling regime is demonstrated by tuning the coupling strength from less than 200 kHz to greater than 40 MHz. This tunable coupling can be used to protect the qubit from cavity-induced relaxation and avoid unwanted qubit-qubit interactions in a multiqubit system.
Srinivasan, S. J.; Hoffman, A. J.; Gambetta, J. M.; Houck, A. A.
t?- and t?-dependence of the bulk-limit superconducting condensation energy of the 2D Hubbard model
The 2D Hubbard model having the 2nd- and 3rd-neighbor transfer energies t? and t? is investigated by use of the variational Monte Carlo method. At the nearly optimal doping with on-site Coulomb energy U=6 (energy unit is t) the condensation energy Econd for the d-wave superconductivity (SC) is computed for lattices of sizes from 10ū10 to 28ū28 with the aim
K. Yamaji; T. Yanagisawa; M. Miyazaki; R. Kadono
Roles of superconducting magnetic bearings and active magnetic bearings in attitude control and energy storage flywheel
Compared with conventional energy storage flywheel, the rotor of attitude control and energy storage flywheel (ACESF) used in space not only has high speed, but also is required to have precise and stable direction. For the presented superconducting magnetic bearing (SMB) and active magnetic bearing (AMB) suspended ACESF, the rotor model including gyroscopic couples is established originally by taking the properties of SMB and AMB into account, the forces of SMB and AMB are simplified by linearization within their own neighbors of equilibrium points. For the high-speed rigid discal rotor with large inertia, the negative effect of gyroscopic effect of rotor is prominent, the radial translation and tilting movement of rotor suspended by only SMB, SMB with equivalent PMB, or SMB together with PD controlled AMB are researched individually. These analysis results proved originally that SMB together with AMB can make the rotor be stable and make the radial amplitude of the vibration of rotor be small while the translation of rotor suspended by only SMB or SMB and PM is not stable and the amplitude of this vibration is large. For the stability of the high-speed rotor in superconducting ACESF, the AMB can suppress the nutation and precession of rotor effectively by cross-feedback control based on the separated PD type control or by other modern control methods.
Tang, Jiqiang; Fang, Jiancheng; Ge, Shuzhi Sam
Magnetic Properties of Iron Chalcogenide Superconducting Materials for Energy Storage Applications
A superconductor is characterized by its ability to conduct electricity without loss and expel magnetic flux when exposed to an external magnetic field. Additionally, the smaller the relaxation rate (S=dM/dt), the better the material for energy storage. This research focuses on the recently discovered high-quality, single-crystalline Iron-based superconductors of FeTe1-xSex (x =0.5), with a transition temperature at Tc=14.5K. Standard creep models are used to analyze the data and determine the effective pinning potential. The magnetization relaxation were measured the Superconducting Quantum Interference Device (SQUID). The relaxation rate appears to be independent of field and temperature for fields below 3T and temperatures below 7K. This result shows that the thermally activated flux motion is not as significant as in other high temperature superconductors, hence FeTe1-xSex, can be a candidate for wire development to be used in Superconducting Magnetic Energy Storage systems.
Knock, Destenie; Pough, Korey; Kebede, Abebe; Seifu, Dereje
Full Gap Superconductivity in Ba0.6K0.4Fe2As2 Probed by Muon Spin Rotation
Superfluid density (ns) in the mixed state of an iron pnictide superconductor Ba1-xKxFe2As2 is determined by muon spin rotation for a sample with optimal doping (x=0.4). The temperature dependence of ns is perfectly reproduced using the conventional BCS model for s-wave paring, where the order parameter can be either a single-gap structure with ?=8.35(6) meV [2?/kBTc=5.09(4)] or double-gap structure with ?1=12 meV (fixed) [2?1/kBTc=7.3] and ?2=6.8(3) meV [2?2/kBTc=4.1(2)]. The latter is consistent with the recent result obtained by the angle-resolved photoemission spectroscopy. The large gap parameters (2?/kBTc) indicate the extremely strong coupling of carriers to bosons that mediate the Cooper pairing.
Hiraishi, Masatoshi; Kadono, Ryosuke; Takeshita, Soshi; Miyazaki, Masanori; Koda, Akihiro; Okabe, Hirotaka; Akimitsu, Jun
Superconductivity in an electron band just above the Fermi level: possible route to BCS-BEC superconductivity
Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe0.6Se0.4(Tc = 14.5 K ~ 1.2 meV) in an accessible range below and above the Fermi level(EF) using ultra-high resolution laser angle-resolved photoemission spectroscopy. We uncover an electron band lying just 0.7 meV (~8 K) above EF at the ?-point, which shows a sharp superconducting coherence peak with gap formation below Tc. The estimated superconducting gap ? and Fermi energy indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-coupling BCS-like superconductivity in the hole band. The study identifies the possible route to BCS-BEC superconductivity.
Okazaki, K.; Ito, Y.; Ota, Y.; Kotani, Y.; Shimojima, T.; Kiss, T.; Watanabe, S.; Chen, C.-T.; Niitaka, S.; Hanaguri, T.; Takagi, H.; Chainani, A.; Shin, S.
Temperature dependence of the spectral weight in p- and n-type cuprates: A study of normal state partial gaps and electronic kinetic energy
The optical conductivity of CuO 2 (copper-oxygen) planes in p- and n-type cuprates thin films at various doping levels is deduced from highly accurate reflectivity data. The temperature dependence of the real part ?1 ( ?) of this optical conductivity and the corresponding spectral weight allow to track the opening of a partial gap in the normal state of n-type Pr 2- xCe xCuO 4 (PCCO) but not of p-type Bi 2Sr 2CaCu 2O 8+ ? (BSCCO) cuprates. This is a clear difference between these two families of cuprates, which we briefly discuss. In BSCCO, the change of the electronic kinetic energy EkinŚdeduced from the spectral weightŚat the superconducting transition is found to cross over from a conventional BCS behavior (increase of Ekin below Tc) to an unconventional behavior (decrease of Ekin below Tc) as the free carrier density decreases. This behavior appears to be linked to the energy scale over which spectral weight is lost and goes into the superfluid condensate, hence may be related to Mott physics.
Bontemps, N.; Lobo, R. P. S. M.; Santander-Syro, A. F.; Zimmers, A.
The optical conductivity of CuO{sub 2} (copper-oxygen) planes in p- and n-type cuprates thin films at various doping levels is deduced from highly accurate reflectivity data. The temperature dependence of the real part {sigma} {sub 1} ({omega}) of this optical conductivity and the corresponding spectral weight allow to track the opening of a partial gap in the normal state of n-type Pr{sub 2-x}Ce {sub x}CuO{sub 4} (PCCO) but not of p-type Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (BSCCO) cuprates. This is a clear difference between these two families of cuprates, which we briefly discuss. In BSCCO, the change of the electronic kinetic energy E {sub kin}-deduced from the spectral weight-at the superconducting transition is found to cross over from a conventional BCS behavior (increase of E {sub kin} below T {sub c}) to an unconventional behavior (decrease of E {sub kin} below T {sub c}) as the free carrier density decreases. This behavior appears to be linked to the energy scale over which spectral weight is lost and goes into the superfluid condensate, hence may be related to Mott physics.
Bontemps, N. [Laboratoire de Physique du Solide (UPR5 CNRS), 10 rue Vauquelin, 75231 Paris cedex 05 (France)]. E-mail: firstname.lastname@example.com; Lobo, R.P.S.M. [Laboratoire de Physique du Solide (UPR5 CNRS), 10 rue Vauquelin, 75231 Paris cedex 05 (France); Santander-Syro, A.F. [Laboratoire de Physique des Solides Universite Paris-Sud, 91405 Orsay (France); Zimmers, A. [Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, MD 20742 (United States)
High-Energy Emission From the Polar Cap and Slot Gap
Thirty-five years after the discovery of rotation-powered pulsars, we still do not understand the fundamentals of their pulsed emission at any wavelength. I will review the latest developments in understanding the high-energy emission of rotation-powered pulsars, with particular emphasis on the polar cap and slot gap models. Special and general relativistic effects play important roles in pulsar emission, from inertial frame-dragging near the stellar surface to aberration, time-of-flight and retardation of the magnetic field near the light cylinder. Understanding how these effects determine what we observe at different wavelengths is critical to unraveling the emission physics. I will discuss how the next generation of gamma-ray detectors, AGILE and GLAST, will test prediction of these models.
Harding, Alice K.
Spin-polarized energy gap opening in asymmetric bilayer graphene nanoribbons
Electronic and magnetic properties of bilayer zigzag graphene nanoribbon (bZGNR) are studied with the use of pseudopotential density functional method. The edge atoms in the top and bottom layers of bZGNR make a weak hybridization, which leads to band dispersion and magnetization different from monolayer ZGNR. For asymmetric bZGNR, where the top and bottom layers have different width, one edge is pinched by the interlayer bonding and the other edge sustains anti-ferromagnetic spin polarization. A small amount of charge transfer occurs from narrower to wider layer, and the band structure for each spin near the Fermi level exhibits an asymmetry. External electric field perpendicular to asymmetric bZGNR produces different energy-gap opening for each spin component, inducing half- metallicity.
Kim, Gyubong; Jhi, Seung-Hoon
A modified simplified coherent potential approximation model of band gap energy of III-V ternary alloys
Based on the modification of the simplified coherent potential approximation (SCPA), a model is developed to calculate the composition dependence of the band gap energy of III-V ternary alloys with the same anion. The derived equation is used to fit the experimental band gap energy of In x Al1- x N, In x Ga1- x N and Al x Ga1- x N with x from 0 to 1. It is found that the fitting results are better than those done by using SCPA. The fitting results are also better than those obtained by using the formula with a small bowing coefficient, especially for In x Al1- x N. In addition, our model can also be used to describe the composition dependence of band gap energy of other III-V ternary alloys.
Zhao, ChuanZhen; Zhang, Rong; Liu, Bin; Fu, DeYi; Li, Ming; Xiu, XiangQian; Xie, ZiLi; Zheng, YouDou
Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy.
In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi2Sr2CaCu2O8+? crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T ? Tc, thus showing that phase coherence and gap formation are distinct processes which occur on different timescales. PMID:25014162
Madan, I; Kurosawa, T; Toda, Y; Oda, M; Mertelj, T; Kusar, P; Mihailovic, D
Separating pairing from quantum phase coherence dynamics above the superconducting transition by femtosecond spectroscopy
In classical superconductors an energy gap and phase coherence appear simultaneously with pairing at the transition to the superconducting state. In high-temperature superconductors, the possibility that pairing and phase coherence are distinct and independent processes has led to intense experimental search of their separate manifestations. Using femtosecond spectroscopy methods we now show that it is possible to clearly separate fluctuation dynamics of the superconducting pairing amplitude from the phase relaxation above the critical transition temperature. Empirically establishing a close correspondence between the superfluid density measured by THz spectroscopy and superconducting optical pump-probe response over a wide region of temperature, we find that in differently doped Bi2Sr2CaCu2O8+? crystals the pairing gap amplitude monotonically extends well beyond Tc, while the phase coherence shows a pronounced power-law divergence as T ? Tc, thus showing that phase coherence and gap formation are distinct processes which occur on different timescales.
Madan, I.; Kurosawa, T.; Toda, Y.; Oda, M.; Mertelj, T.; Kusar, P.; Mihailovic, D.
Operational experience with a superconducting magnetic energy storage device at Owens Corning Vinyl Operations, Fair Bluff, North Carolina
This paper presents the operational and power quality monitoring results for 21 months operating experience of a superconducting magnetic energy storage (SMES) device used to mitigate power quality disturbances at the Owens Coming Vinyl Operations in Fair Bluff, North Carolina, USA, a vinyl siding manufacturer. The SMES unit at Owens Coming provides sag and momentary interruption ride-through for the plant's
John Cerulli; G. Melotte; S. Peele
Study on current source type superconducting magnetic energy storage based on PSCAD\\/EMTDC for the stability of power system
Use current source type superconducting magnetic energy storage (CSMES), a time-domain simulation model founded under the environment of PSCAD\\/EMTDC, to connect to several power systems to verify its good performance on voltage damp, transient stability, sub transient stability. Experimental results show that the model for enhancing the stability of the power system has apparent accomplishment.
Zhang Wei; Xiang Tie-yuan; Hu Wei
Phenomenology of the normal and superconducting states of a marginal Fermi liquid (invited)
A metal with scattering from a flat frequency spectrum of particle-hole pairs is a marginal'' Fermi liquid, with infinite quasiparticle lifetime but a logarithmically vanishing spectral weight. In the superconducting state, the scattering spectrum should acquire a gap, and the quasiparticle character will be restored at low energies. Unless the scattering spectrum results from interband processes, the Drude-like component of the optical conductivity will then have an onset at 4{Delta} in the clean limit, twice the superconducting gap. Other experimental ramifications, in particular for tunnelling, NMR relaxation rate, thermal conductivity, and photoemission spectra are considered.
Littlewood, P.B.; Varma, C.M. (AT T Bell Laboratories, Murray Hill, New Jersey 07974 (US))
Overruling the energy gap law: fast triplet formation in 6-azauracil.
The photophysical properties of 6-azauracil were studied by means of ab initio quantum chemical methods. On the basis of our calculations we propose here the following mechanism for the lack of fluorescence and the high triplet quantum yield that was observed experimentally after irradiation of this compound with UV light [Kobayashi et al., J. Phys. Chem. A, 2008, 112, 13308]. Multiple potential energy surface crossings between excited singlet states of ???* and n??* character lead to an ultrafast transfer of the S(2) ((1)???*) population to the lower-lying S(1) ((1)n??*) state. This state acts as a doorway state from which the T(1) ((3)???*) state is formed approximately within 125 ps in the isolated 6-azauracil and within 30 ps in acetonitrile solution according to our calculations. The enhancement of the S(1)[radiolysis arrow - arrow with voltage kink] T(1) intersystem crossing in acetonitrile solution is noteworthy as it goes along with an increased adiabatic energy gap between the interacting states. Blue shift of the S(1) potential energy surface by about 0.2 eV in this polar, aprotic environment places the intersection between the S(1) and T(1) potentials close to the S(1) minimum, thus increasing the overlap of the vibrational wavefunctions and consequently speeding up the spin-forbidden nonradiative transition. PMID:20680213
Etinski, Mihajlo; Marian, Christel M
Narrow energy gap between triplet and singlet excited states of Sn2+ in borate glass.
Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns(2)-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn(2+)-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors. PMID:24345869
Masai, Hirokazu; Yamada, Yasuhiro; Suzuki, Yuto; Teramura, Kentaro; Kanemitsu, Yoshihiko; Yoko, Toshinobu
Narrow Energy Gap between Triplet and Singlet Excited States of Sn2+ in Borate Glass
Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns2-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn2+-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors.
Surface Plasmon-Mediated Energy Transfer in Hetero-Gap Au-Ag Nanowires
We report the observation of energy transfer from a gold (Au) nanodisk pair to a silver (Ag) nanowire across a 120 nm gap via surface plasmon resonance (SPR) excitation. The enhanced electromagnetic (EM) fields generated by Au SPR excitation induce oscillation of the conduction electrons in the Ag segment, transferring energy to it even though the Ag segment has only weak resonant interactions with the incident electromagnetic radiation. The induced Ag SPR produces strong EM fields at the position of the Ag segment, leading to a Raman signal ~15 times greater than when the Ag segment is alone (not adjacent to the Au nanodisk pair). The Raman intensity is found to depend nonlinearly on the incident laser intensity for laser power densities of 10 kW/cm2, which is consistent with the results of electromagnetic theory calculations which are not able to account for the factor of 15 enhancement based on a linear mechanism. This suggests that energy transfer from the Au disk pair to the Ag segment involves an enhanced nonlinear polarization mechanism such as can be produced by the electronic Kerr effect or stimulated Raman scattering.
Wei, Wei; Li, Shuzhou; Qin, Lidong; Xue, Can; Millstone, Jill E.; Xu, Xiaoyang; Schatz, George C.; Mirkin, Chad A.
Joint operation of the superconducting fault current limiter and magnetic energy storage system in an electric power network
An opportunity of using superconductors as active elements of electric power systems designed to control the electric power distribution, to enhance the systems operating modes and to limit fault currents, was very attractive for investigators for a long time. In this paper, is considered an opportunity to enhance the electric power systems with the aid of superconducting magnetic energy storage systems (SMES) and superconducting fault current limiters (SFCL) operating together. It has been shown that the joint operation of both these superconducting devices allows additional varying of their parameters, what in turn gives a further opportunity to reduce their mass and dimensions and consequently the costs. There had been also shown an additional advantage of the SMES and SFCL joint operation consisting in that they ensure a more effective protection for a power system, preventing its uncontrolled load-off and subsequent acceleration up to the inaccessible rotation speed.
Kopylov, S. I.; Balashov, N. N.; Ivanov, S. S.; Veselovsky, A. S.; Zhemerikin, V. D.
One of the frontiers in FEL science is that of high power. In order to reach power in the megawatt range, one requires a current of the order of one ampere with a reasonably good emittance. The superconducting laser-photocathode RF gun with a high quantum efficiency photocathode is the most natural candidate to provide this performance. The development of a 1/2 cell superconducting photoinjector designed to operate at up to a current of 0.5 amperes and beam energy of 2 MeV and its photocathode system are the subjects covered in this paper. The main issues are the photocathode and its insertion mechanism, the power coupling and High Order Mode damping. This technology is being developed at BNL for DOE nuclear physics applications such as electron cooling at high energy and electron ion colliders..
Evaluation method of power rating and energy capacity of Superconducting Magnetic Energy Storage system for output smoothing control of wind farm
This paper proposes a system composed of a wind turbine generator system and superconducting magnetic energy storage (SMES) unit, in which SMES is controlled for smoothing the wind generator output power. A determination of power rating and storage energy capacity of SMES unit which are sufficient for the smoothing control but as small as possible is very important problem. In
Tomoki Asao; Rion Takahashi; Toshiaki Murata; Junji Tamura; Masahiro Kubo; Yoshiharu Matsumura; Akira Kuwayama; Takatoshi Matsumoto
Influence of Weak Self-Field Effect on Calculated Activation Energy for Superconducting Thin Film
When the applied field Ba = ?0Ha (Ha > Hp) is perpendicular to the surface of a disk-shaped superconducting thin film with the full penetrated field Hp, the radius R, and the thickness d, a quantitative relation between the average field langBrang and the magnetization M is described by langBrang = ?0[Ha + (0.81 d/R) M] for R gg d, where the term ?0(0.81 d/R) M also is the average self-field of the film. Combining this relation with the magnetic flux conservation equation and the Arrhenius relation, the effective activation energy is extracted from the experimental magnetization relaxation and the dynamic magnetization relaxation, respectively.
Xu, Xiao-nong; Sun, Ai-min; Ding, Shi-ying; Jin, Xin; Yao, Xi-xian; Yan, Shao-lin; Wen, Hai-hu
Solving LFC problem in an interconnected power system using superconducting magnetic energy storage
This paper proposes the combination of a load frequency control (LFC) with superconducting magnetic energy storage (SMES) to solve the LFC problem in interconnected power systems. By using this combination, the speed damping of frequency and tie-line power flow deviations is considerably increased. A new control strategy of SMES is proposed in this paper. The problem of determining optimal parameters of PID and SMES control loop is considered as an optimization problem and a pattern search algorithm (PS) optimization is employed to solve it. The simulation results show that if an SMES unit is installed in an interconnected power system, in addition to eliminating oscillations and deviations, the settling time in the frequency and tie-line power flow responses is considerably reduced.
Farahani, Mohsen; Ganjefar, Soheil
Design of an accelerating cavity for the Superconducting Super Collider Low-Energy Booster
This paper presents the history and current status of the design of the accelerator cavity to be incorporated into the Low-Energy Booster (LEB) of the Superconducting Super Collider (SSC). The LEB is a proton synchrotron, 540 meters in circumference, and having 108 buckets around the ring. Acceleration programs, each 50 msec long, take place at a rate of 10 per second. The beta change of the particles from injection to extraction is from 0.8 to 0.997. Since the rf excitation frequency must track beta, the rf frequency must shift from 47.5 to 60 MHz over the 50-msec acceleration program. The cavity will use ferrite in a perpendicular control bias mode to effect the require tuning. 4 refs., 1 fig.
Friedrichs, C.C.; Walling, L. (Los Alamos National Lab., NM (USA)); Campbell, B.M. (Superconducting Super Collider Lab., Dallas, TX (USA))
Interlayer Superconducting Pairing Induced c-axis Nodal Lines in Iron-based Superconductors
A layered superconductor with a full pairing energy gap can be driven into a nodal superconducting (SC) state by inter-layer pairing when the SC state becomes more quasi-3D. We propose that this mechanism is responsible for the observed nodal behavior in a class of iron-based SCs. We show that the intra- and inter-layer pairings generally compete and the gap nodes
Yuehua Su; Chandan Setty; Ziqiang Wang; Jiangping Hu
We present the results of our investigation of lead and niobium as suitable photocathode materials for superconducting RF injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and a variety of cathode preparation methods, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.
Conceptual design study of superconducting magnetic energy storage using high temperature superconductors. Final report
Since the discovery of high critical temperature superconductors (HTS), many predictions have been made for savings in the cost or performance of superconducting technologies for electric utility systems, such as superconducting magnetic energy storage (SMES). The higher operating temperature of HTS materials could mean the use of less expensive cryogens, such as liquid nitrogen, higher refrigeration efficiencies, greater reliability, and easier acceptance within the utility community. While all of these developments may occur, the significance of the improvements depends on the application and other characteristics of the system. Also, today`s HTS materials have some negative features, including lower critical current density and greater brittleness, compared to conventional metallic superconductors. A conceptual design for SMES using HTS has been analyzed to determine configuration parameters, refrigeration requirements, and estimated costs of major components. The study covered the energy storage range from 2 to 200 MWh at power levels from 4 to 400 MW. This range includes utility applications from transient and power stabilization to spinning reserve and load leveling. The present assessment has been carried out for cold-supported modular torus and for comparison, a cold-supported modular solenoid. The toroidal configuration was chosen for analysis because it has minimal magnetic field, which could be an advantage in locating a small unit near a utility or customer load. The comparison shows that for all cases, the solenoid is comparable in price or less expensive. However, the solenoid has a varying external magnetic field which must be accommodated. The modular approach was selected primarily as a way to wind the coil and keep the brittle oxide superconductor under compression at all operating conditions to avoid breakage.
Schoenung, S.M.; Meier, W.R. [Schafer (W.J.) Associates, Inc., Pleasanton, CA (United States); Fagaly, R.L.; Heiberger, M.; Stephens, R.B.; Leuer, J.A.; Guzman, R.A.; Johnson, E.R. [General Atomics, San Diego, CA (United States); Purcell, J.; Creedon, L. [Advanced CryoMagnetics, Inc., San Diego, CA (United States); Hull, J.R. [Argonne National Lab., IL (United States)
Conceptual design study of superconducting magnetic energy storage using high temperature superconductors
Since the discovery of high critical temperature superconductors (HTS), many predictions have been made for savings in the cost or performance of superconducting technologies for electric utility systems, such as superconducting magnetic energy storage (SMES). The higher operating temperature of HTS materials could mean the use of less expensive cryogens, such as liquid nitrogen, higher refrigeration efficiencies, greater reliability, and easier acceptance within the utility community. While all of these developments may occur, the significance of the improvements depends on the application and other characteristics of the system. Also, today's HTS materials have some negative features, including lower critical current density and greater brittleness, compared to conventional metallic superconductors. A conceptual design for SMES using HTS has been analyzed to determine configuration parameters, refrigeration requirements, and estimated costs of major components. The study covered the energy storage range from 2 to 200 MWh at power levels from 4 to 400 MW. This range includes utility applications from transient and power stabilization to spinning reserve and load leveling. The present assessment has been carried out for cold-supported modular torus and for comparison, a cold-supported modular solenoid. The toroidal configuration was chosen for analysis because it has minimal magnetic field, which could be an advantage in locating a small unit near a utility or customer load. The comparison shows that for all cases, the solenoid is comparable in price or less expensive. However, the solenoid has a varying external magnetic field which must be accommodated. The modular approach was selected primarily as a way to wind the coil and keep the brittle oxide superconductor under compression at all operating conditions to avoid breakage.
Schoenung, S.M.; Meier, W.R. (Schafer (W.J.) Associates, Inc., Pleasanton, CA (United States)); Fagaly, R.L.; Heiberger, M.; Stephens, R.B.; Leuer, J.A.; Guzman, R.A.; Johnson, E.R. (General Atomics, San Diego, CA (United States)); Purcell, J.; Creedon, L. (Advanced CryoMagnetics, Inc., San Diego, CA (United States)); Hull, J.R. (Argonne National Lab., IL (United States))
Analysis of superconducting magnetic energy storage applications at a proposed wind farm site near Browning, Montana
A computer program was developed to analyze the viability of integrating superconducting magnetic energy storage (SMES) with proposed wind farm scenarios at a site near Browning, Montana. The program simulated an hour-by-hour account of the charge/discharge history of a SMES unit for a representative wind-speed year. Effects of power output, storage capacity, and power conditioning capability on SMES performance characteristics were analyzed on a seasonal, diurnal, and hourly basis. The SMES unit was assumed to be charged during periods when power output of the wind resource exceeded its average value. Energy was discharged from the SMES unit into the grid during periods of low wind speed to compensate for below-average output of the wind resource. The option of using SMES to provide power continuity for a wind farm supplemented by combustion turbines was also investigated. Levelizing the annual output of large wind energy systems operating in the Blackfeet area of Montana was found to require a storage capacity too large to be economically viable. However, it appears that intermediate-sized SMES economically levelize the wind energy output on a seasonal basis.
Gaustad, K. L.; Desteese, J. G.
Effect of hydrostatic pressure on superconducting lead--indium alloys using electron tunneling
The effect of pressure on the effective phonon spectrnm alpha ( omega ; (F( omega ), the dimensionless electron--phonon interaction strength lambda , ; and the average electron-phonon coupling function ( alpha ┬▓) was determined ; in the superconducting alloys PbŌŌInŌ and PbŌŌInŌüŌ. ; Electro n-tunneling measurements at pressures from 0 to 3600 bar provided the ; energy gap and
H. H. Hansen; R. L. Pompi; T. M. Wu
Superconducting transmission line particle detector
A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.
Gray, K.E.
Energy losses in superconductive DC-electromagnets due to ferromagnetic movement
A DC-current, superconductive electromagnet is a source of the magnetic field in a separator matrix. This type of separator operates in a cyclic way. Therefore, it appears as very important to ensure the electromagnet stability during operation, i.e., range of parameters` changes that could maintain the magnet winding in the superconductive state. This means selecting parameter changes representing the magnet winding in the superconductive state.
Ciesla, A.; Matras, A. [Univ. of Mining and Metallurgy, Krakow (Poland)] [Univ. of Mining and Metallurgy, Krakow (Poland)
Nuclear spin-lattice relaxation of 139La in the superconducting phase of La1.8Sr0.2CuO4- delta
We report on zero-field nuclear spin-lattice relaxation measurements of 139La in La1.8Sr0.2CuO4-? in the normal and the superconducting state. Below the superconducting transition temperature Tc the relaxation rate behaves like 1\\/T1 ? exp [- ?\\/kT] with activation energy ? = 11.5 meV leading to a gap energy of 2? = 23 meV. With Tc = 38 K the ratio 2?\\/kTc
H. Seidel; F. Hentsch; M. Mehring; J. G. Bednorz; K. A. M³ller
Electric-field control of the band gap and Fermi energy in graphene multilayers by top and back gates
It is known that a perpendicular electric field applied to multilayers of graphene modifies the electronic structure near the K point and may induce an energy gap in the electronic spectrum which is tunable by the gate voltage. Here we consider a system of graphene multilayers in the presence of a positively charged top and a negatively charged back gate
A. A. Avetisyan; B. Partoens; F. M. Peeters
Self-energy effects in cuprates and the dome-shaped behavior of the superconducting critical temperature
Hole-doped cuprates show a superconducting critical temperature Tc which follows a universal dome-shaped behavior as a function of doping. It is believed that the origin of superconductivity in cuprates is entangled with the physics of the pseudogap phase. An open discussion is whether the source of superconductivity is the same effect that causes the pseudogap properties. The t-J model treated in large-N expansion shows d-wave superconductivity triggered by nonretarded interactions, and an instability of the paramagnetic state to a flux phase or d-wave charge-density wave (d-CDW) state. In this paper we show that self-energy effects near the d-CDW instability may lead to a dome-shaped behavior of Tc. In addition, it is also shown that these self-energy contributions may describe several properties observed in the pseudogap phase. In this picture, although fluctuations responsible for the pseudogap properties lead to a dome-shaped behavior, they are not involved in pairing, which is mainly nonretarded.
Buzon, Guillermo; Foussats, Adriana; Bejas, MatĒas; Greco, Andrķs
Coherent suppression of electromagnetic dissipation due to superconducting quasiparticles
Owing to the low-loss propagation of electromagnetic signals in superconductors, Josephson junctions constitute ideal building blocks for quantum memories, amplifiers, detectors and high-speed processing units, operating over a wide band of microwave frequencies. Nevertheless, although transport in superconducting wires is perfectly lossless for direct current, transport of radio-frequency signals can be dissipative in the presence of quasiparticle excitations above the superconducting gap. Moreover, the exact mechanism of this dissipation in Josephson junctions has never been fully resolved experimentally. In particular, Josephson's key theoretical prediction that quasiparticle dissipation should vanish in transport through a junction when the phase difference across the junction is ? (ref. 2) has never been observed. This subtle effect can be understood as resulting from the destructive interference of two separate dissipative channels involving electron-like and hole-like quasiparticles. Here we report the experimental observation of this quantum coherent suppression of quasiparticle dissipation across a Josephson junction. As the average phase bias across the junction is swept through ?, we measure an increase of more than one order of magnitude in the energy relaxation time of a superconducting artificial atom. This striking suppression of dissipation, despite the presence of lossy quasiparticle excitations above the superconducting gap, provides a powerful tool for minimizing decoherence in quantum electronic systems and could be directly exploited in quantum information experiments with superconducting quantum bits.
Pop, Ioan M.; Geerlings, Kurtis; Catelani, Gianluigi; Schoelkopf, Robert J.; Glazman, Leonid I.; Devoret, Michel H.
Coherent suppression of electromagnetic dissipation due to superconducting quasiparticles.
Owing to the low-loss propagation of electromagnetic signals in superconductors, Josephson junctions constitute ideal building blocks for quantum memories, amplifiers, detectors and high-speed processing units, operating over a wide band of microwave frequencies. Nevertheless, although transport in superconducting wires is perfectly lossless for direct current, transport of radio-frequency signals can be dissipative in the presence of quasiparticle excitations above the superconducting gap. Moreover, the exact mechanism of this dissipation in Josephson junctions has never been fully resolved experimentally. In particular, Josephson's key theoretical prediction that quasiparticle dissipation should vanish in transport through a junction when the phase difference across the junction is ? (ref. 2) has never been observed. This subtle effect can be understood as resulting from the destructive interference of two separate dissipative channels involving electron-like and hole-like quasiparticles. Here we report the experimental observation of this quantum coherent suppression of quasiparticle dissipation across a Josephson junction. As the average phase bias across the junction is swept through ?, we measure an increase of more than one order of magnitude in the energy relaxation time of a superconducting artificial atom. This striking suppression of dissipation, despite the presence of lossy quasiparticle excitations above the superconducting gap, provides a powerful tool for minimizing decoherence in quantum electronic systems and could be directly exploited in quantum information experiments with superconducting quantum bits. PMID:24740067
Pop, Ioan M; Geerlings, Kurtis; Catelani, Gianluigi; Schoelkopf, Robert J; Glazman, Leonid I; Devoret, Michel H
Phenomenology of the superconductive state of a marginal Fermi liquid
We consider an extension of the marginal-Fermi-liquid model to the {ital s}-wave superconducting state by phenomenologically incorporating the superconducting gap into the scattering spectrum. The linear-in-temperature scattering rate due to the high density of low-energy electronic excitations naturally leads to a large pair-breaking rate, which suppresses {ital T}{sub {ital c}}. Below {ital T}{sub {ital c}} the low-energy excitations are self-consistently suppressed due to the opening of a superconducting gap. This leads to a vanishing of both the inelastic-scattering rate and pair breaking below {ital T}{sub {ital c}}. There are a number of consequences not found in traditional BCS electron-phonon--induced {ital s}-wave superconductors. For energies below 3{Delta}, the quasiparticles become well defined in the superconducting state, while they are marginal (scattering rate proportional to the energy) in the normal state. This produces a two-peaked structure in the one-particle spectra---a sharp feature between {Delta} and 3{Delta} (depending on momentum) and a broad hump with an onset at 3{Delta} (independent of momentum). The transport properties do not obey the usual BCS rules. Transport properties in the {ital q}{r arrow}0 limit and for low frequencies {omega}{much lt}{Delta} show peaks below {ital T}{sub {ital c}}. These are observable in microwave conductivity and in electronic thermal conductivity. Local or momentum-averaged response properties such as the nuclear relaxation rate show no peak, but a sharp drop below {ital T}{sub {ital c}}. The superconductive gap opens very rapidly below {ital T}{sub {ital c}}, and the value of 2{Delta}/{ital T}{sub {ital c}} can cover a wide range, depending on parameters. The physical origin of these results is discussed, and comparison to experiment is made.
Littlewood, P.B.; Varma, C.M. (AT T Bell Laboratories, Murray Hill, New Jersey 07974 (United States))
Design, performance, and cost characteristics of high temperature superconducting magnetic energy storage
A conceptual design for superconducting magnetic energy storage (SMES) using oxide superconductors with higher critical temperature than metallic superconductors has been analyzed for design features, refrigeration requirements, and estimated costs of major components. The study covered the energy storage range from 2 to 200 MWh at power levels from 4 to 400 MW. A SMES that uses high temperature superconductors (HTS) and operates at high magnetic field (e.g., 10 tesla), can be more compact than a comparable, conventional low-temperature device at lower field. The refrigeration power required for a higher temperature unit (20 to 77 Kelvin) will be less by 60 to 90 percent. The improvement in energy efficiency is significant for small units, but less important for large ones. The material cost for HTS units is dominated by the cost of superconductor, so that the total cost of an HTS system will be comparable to a low temperature system only if the superconductor price in $/Ampere-meter is made comparable by increasing current density or decreasing wire cost.
Schoenung, S.M.; Meier, W.R. (W.J. Schafer Associates, Inc., Pleasanton, CA (United States)); Fagaly, R.L.; Heiberger, M.; Stephens, R.B.; Leuer, J.A.; Guzman, R.A. (General Atomics, San Diego, CA (United States))
Energy resolution and high count rate performance of superconducting tunnel junction x-ray spectrometers
We present experimental results obtained with a cryogenically cooled, high-resolution x-ray spectrometer based on a 141{mu}m{times}141{mu}m Nb-Al-Al{sub 2}O{sub 3}-Al-Nb superconducting tunnel junction (STJ) detector in a demonstration experiment. Using monochromatized synchrotron radiation we studied the energy resolution of this energy-dispersive spectrometer for soft x rays with energies between 70 and 700 eV and investigated its performance at count rates up to nearly 60000 cps. At count rates of several 100 cps we achieved an energy resolution of 5.9 eV (FWHM) and an electronic noise of 4.5 eV for 277 eV x rays (the energy corresponding to C K). Increasing the count rate, the resolution 277 eV remained below 10 eV for count rates up to {approximately}10000cps and then degraded to 13 eV at 23000 cps and 20 eV at 50000 cps. These results were achieved using a commercially available spectroscopy amplifier with a baseline restorer. No pile-up rejection was applied in these measurements. Our results show that STJ detectors can operate at count rates approaching those of semiconductor detectors while still providing a significantly better energy resolution for soft x rays. Thus STJ detectors may prove very useful in microanalysis, synchrotron x-ray fluorescence (XRF) applications, and XRF analysis of light elements (K lines) and transition elements (L lines). {copyright} {ital 1998 American Institute of Physics.}
Frank, M.; Hiller, L.J.; le Grand, J.B.; Mears, C.A.; Labov, S.E.; Lindeman, M.A.; Netel, H.; Chow, D. [Lawrence Livermore National Laboratory, P.O. Box 808, L-401, Livermore, California 94551 (United States)] [Lawrence Livermore National Laboratory, P.O. Box 808, L-401, Livermore, California 94551 (United States); Barfknecht, A. [Conductus, Inc., 969 West Maude Ave., Sunnyvale, California 94086 (United States)] [Conductus, Inc., 969 West Maude Ave., Sunnyvale, California 94086 (United States)
Evaluation of BandGap Energies and Characterization of Nonradiative Recombination Centers of Film and Bulk GaN Crystals
We have measured photothermal spectra of bulk and film GaN crystals by the photothermal divergence (PTD) method in the temperature range from 110 K to 320 K. The band-gap energy of the GaN film grown by metalorganic chemical vapor deposition (MOCVD) method on a sapphire substrate shifts toward a higher energy because of the stress, compared with that of the
Masaru Kamano; Masanobu Haraguchi; Masuo Fukui; Minoru Kuwahara; Toshihiro Okamoto; Takashi Mukai; Genichi Shinomiya
Elevated temperature dependence of energy band gap of ZnO thin films grown by e-beam deposition
We report the surface, structural, electronic, and optical properties of the epitaxial ZnO thin films grown on (0001) sapphire substrate at 600 deg. C by an electron-beam deposition technique. ZnO thin films have been deposited in an oxygen environment and post-deposition annealed to improve the stoichiometry and the crystal quality. In order to investigate the free exciton binding energy and the temperature dependence of the energy bandgap, we carried out variable temperature (78-450 K) transmittance measurements on ZnO thin films. The absorption data below the energy bandgap have been modeled with the Urbach tail and a free exciton, while the data above the gap have been modeled with the charge transfer excitations. The exciton binding energy is measured to be E{sub 0}= 64 {+-} 7 meV, and the energy band gaps of the ZnO film are measured to be E{sub g}-tilde 3.51 and 3.48 eV at 78 and 300 K, respectively. The temperature dependence of the energy gap has been fitted with the Varshni model to extract the fitting parameters {alpha}= 0.00020 {+-} 0.00002 eV/K, {beta}= 325 {+-} 20 K, and E{sub g} (T = 0 K) = 3.516 {+-} 0.0002 eV.
Rai, R. C.; Guminiak, M.; Wilser, S. [Department of Physics, SUNY College at Buffalo, Buffalo, New York 14222 (United States); Cai, B.; Nakarmi, M. L. [Department of Physics, Brooklyn College of the CUNY, Brooklyn, New York 11210 (United States)
Restoration of the Derivative Discontinuity in Kohn-Sham Density Functional Theory: An Efficient Scheme for Energy Gap Correction
From the perspective of perturbation theory, we propose a systematic procedure for the evaluation of the derivative discontinuity (DD) of the exchange-correlation energy functional in Kohn-Sham (KS) density functional theory, wherein the exact DD can in principle be obtained by summing up all the perturbation corrections to infinite order. Truncation of the perturbation series at low order yields an efficient scheme for obtaining the approximate DD. While the zeroth-order theory yields a vanishing DD, the first-order correction to the DD can be expressed as an explicit universal functional of the ground-state density and the KS lowest unoccupied molecular orbital density, allowing the direct evaluation of the DD in the standard KS method without extra computational cost. The fundamental gap can be predicted by adding the estimated DD to the KS gap. This scheme is shown to be accurate in the prediction of the fundamental gaps for a wide variety of atoms and molecules.
Chai, Jeng-Da; Chen, Po-Ta
Individual thin fibers of NbTi (46.5 wt % Ti) have been driven from the superconducting to the normal state by tensile force while immersed in liquid helium and carrying subcritical currents. The additional force for successive excursions from the superconducting to the normal state has been measured and found to saturate. This ''mechanical training'' can be reduced to the starting
L. S. Wright; H. Wiederick; T. Hutchison
Ultrasonic investigation of the superconducting properties of the Nb-Mo system
The superconducting properties of single crystals of Nb and two alloys of Nb with Mo were investigated by ultrasonic techniques. The results of measurements of the ultrasonic attenuation and velocities as a function of temperature, Mo composition, crystallographic direction, and ultrasonic frequency are reported. The attenuation and small velocity changes associated with the superconductivity of the samples are shown to be dependent on the sample resistivity ratio which varied from 4.3 for Nb-9% Mo to 6500 for pure Nb. The ultrasonic attenuation data are analyzed in terms of the superconducting energy gap term of the BCS theory. A new model is proposed for the analysis of ultrasonic attenuation in pure superconductors with two partially decoupled energy bands. To analyze the attenuation in pure superconducting Nb, the existence of two energy gaps was assumed to be associated with the two partially decoupled energy bands. One of the gaps was found to have the normal BCS value of 3.4 and the other gap was found to have the anomalously large value of 10. No experimental evidence was found to suggest that the second energy gap had a different transition temperature. The interpretation of the results for the Nb-Mo alloys is shown to be complicated by the possible existence of a second superconducting phase in Nb-Mo alloys with a transition temperature of 0.35 of the transition temperature of the first phase. The elastic constants of Nb and Nb-Mo alloys are shown to be approximately independent of Mo composition to nine atomic percent Mo. These results do not agree with the current microscopic theory of transition temperature for the transition elements.
Lacy, L. L.
Evidence of a Nonequilibrium Distribution of Quasiparticles in the Microwave Response of a Superconducting Aluminum Resonator
In a superconductor, absorption of photons with an energy below the superconducting gap leads to redistribution of quasiparticles over energy and thus induces a strong nonequilibrium quasiparticle energy distribution. We have measured the electrodynamic response, quality factor, and resonant frequency of a superconducting aluminium microwave resonator as a function of microwave power and temperature. Below 200 mK, both the quality factor and resonant frequency decrease with increasing microwave power, consistent with the creation of excess quasiparticles due to microwave absorption. Counterintuitively, above 200 mK, the quality factor and resonant frequency increase with increasing power. We demonstrate that the effect can only be understood by a nonthermal quasiparticle distribution.
de Visser, P. J.; Goldie, D. J.; Diener, P.; Withington, S.; Baselmans, J. J. A.; Klapwijk, T. M.
Effects of potting on training and quench propagation in a large stored energy superconducting dipole coil
A superconducting racetrack dipole coil was constructed to compare directly training and quench behavior in potted and non-potted coils. The stored energy of this coil was 175 KJoules at the conductor's short sample limit of 238 Amp with a peak field on the coil of 7.6 Tesla. The outward magnetic forces were restrained by rows of tie rods between side plates. Comparisons of training behavior were made for both steel and aluminum tie rods. Helium flow was provided by channels in the fiberglass cable tape allowing 1/4 of the conductor direct access to the helium supply. After training the coil to 90% of short sample limit, the tie rods were relaxed and the entire coil was vacuum impregnated with a standard clear magnet epoxy. After potting, the previous tie rod preloads were re-established. This resulted in a much shallower training curve, and required retraining after thermal cycling. The unpotted coil showed no evidence of internal quench propagation below 80% short sample, whereas the potted coil exhibited good quench propagation and energy dissipation at all currents, simplifying protection strategies. Fully impregnated coils of this design are not practical for thermally cycled magnets designed to operate above 80% of short sample limit.
Cox, B.; Garbincius, P.H.; Guerra, J.; Mazur, P.O.; Satti, J.A.; Tilles, E.B.
Superconductive connection
A superconductive connection between two superconductive members, one or both of which members are niobium, is effectuated utilizing a solder chosen from the group consisting of indium--lead alloys and indium--bismuth alloys. In making the superconducting connection, molten solder preferably is rubbed onto the niobium surface utilizing a metal brush and the other superconductive member subsequently is pressed against the molten
Operation of the 30 MJ superconducting magnetic energy storage system in the Bonneville Power Administration Electrical Grid
The 30 MJ superconducting magnetic energy storage (SMES) system was installed in the Bonneville Power Administration (BPA) Tacoma Substation in 1982 to 1983. Operation of the unit since that time has been for over 1200 hours. Specific tests to explore the SMES system's thermal and electrical characteristics and the control functions were conducted. The coil heat load with current modulation was determined. A converter with two 6-pulse bridges interfaces the superconducting coil to the power bus. Equal bridge voltage amplitude and constant reactive power modes of operation of the system were run with computer control of the SCR bridge firing angles. Coil energy dump tests were performed. Electrical grid system response to SMES modulation was observed, and full power SMES modulation was undertaken.
Rogers, J.D.; Boenig, H.J.; Schermer, R.I.; Hauer, J.F.
Superconductivity and ferromagnetism in topological insulators
Topological insulators, a new state of matter discovered recently, have attracted great interest due to their novel properties. They are insulating inside the bulk, but conducting at the surface or edges. This peculiar behavior is characterized by an insulating bulk energy gap and gapless surface or edge states, which originate from strong spin-orbit coupling and time-reversal symmetry. The spin and momentum locked surface states not only provide a model system to study fundamental physics, but can also lead to applications in spintronics and dissipationless electronics. While topological insulators are interesting by themselves, more exotic behaviors are predicted when an energy gap is induced at the surface. This dissertation explores two types of surface state gap in topological insulators, a superconducting gap induced by proximity effect and a magnetic gap induced by chemical doping. The first three chapters provide introductory theory and experimental details of my research. Chapter 1 provides a brief introduction to the theoretical background of topological insulators. Chapter 2 is dedicated to material synthesis principles and techniques. I will focus on two major synthesis methods: molecular beam epitaxy for the growth of Bi2Se3 thin films and chemical vapor deposition for the growth of Bi2Se3 nanoribbons and nanowires. Material characterization is discussed in Chapter 3. I will describe structural, morphological, magnetic, electrical, and electronic characterization techniques used to study topological insulators. Chapter 4 discusses the experiments on proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons. This work is motivated by the search for the elusive Majorana fermions, which act as their own antiparticles. They were proposed by Ettore Majorara in 1937, but have remained undiscovered. Recently, Majorana's concept has been revived in condensed matter physics: a condensed matter analog of Majorana fermions is predicted to exist when topological insulators are interfaced with superconductors. The observation of Majorana fermions would not only be fundamentally important, but would also lead to applications in fault-tolerant topological quantum computation. By interfacing topological insulator nanoribbons with superconducting electrodes, we observe distinct signatures of proximity-induced superconductivity, which is found to be present in devices with channel lengths that are much longer than the normal transport characteristic lengths. This might suggest preferential coupling of the proximity effect to a ballistic surface channel of the topological insulator. In addition, when the electrodes are in the superconducting state, we observe periodic magnetoresistance oscillations which suggest the formation of vortices in the proximity-induced region of the nanoribbons. Our results demonstrate that proximity-induced superconductivity and vortices can be realized in our nanoribbon geometry, which accomplishes a first important step towards the search for Majorana fermions in condensed matter. In Chapter 5, I will discuss experiments on a magnetically-doped topological insulator (Mn-doped Bi2Se3) to induce a surface state gap. The metallic Dirac cone surface states of a topological insulator are expected to be protected against small perturbations by time-reversal symmetry. However, these surface states can be dramatically modified and a finite energy gap can be opened at the Dirac point by breaking the time-reversal symmetry via magnetic doping. The interplay between magnetism and topological surface states is predicted to yield novel phenomena of fundamental interest such as a topological magneto-electric effect, a quantized anomalous Hall effect, and the induction of magnetic monopoles. Our systematic measurements reveal a close correlation between the onset of ferromagnetism and quantum corrections to diffusive transport, which crosses over from the symplectic (weak anti-localization) to the unitary (weak localization) class. A comprehensive interpretation of data obtained from elec
Zhang, Duming
A large air gap flat transformer for a transcutaneous energy transmission system
A flat transformer for a full-bridge series resonant DC\\/DC power converter which transfers several W of power across a large, variable human skin gap has been designed and built, The power converter can power a rechargeable cardiac pacemaker battery through intact skin by utilizing a transformer with an air gap of 0.5 to 1.5 cm between the primary and the
Toshi Hiro Nishimura; Tetsuji Eguchi; Katsuya Hirachi; Yasushi Maejima; K. Kuwana; Masao Saito
A linear matrix inequality approach to robust damping control design in power systems with superconducting magnetic energy storage device
This paper presents a systematic design procedure for a robust damping controller based on the linear matrix inequality (LMI) approach employing a superconducting magnetic energy storage (SMES) device. The design procedure takes advantage of the multi-objective features of LMI based design techniques. The procedure is applied to enhance the damping of inter-area oscillations in a two-area four-machine test system
Bikash C. Pal; Alun A. Coonick; Imad M. Jaimoukha; Haitham El-Zobaidi
Basic Research Needs for Superconductivity. Report of the Basic Energy Sciences Workshop on Superconductivity, May 8-11, 2006.
As an energy carrier, electricity has no rival with regard to its environmental cleanliness, flexibility in interfacing with multiple production sources and end uses, and efficiency of delivery. In fact, the electric power grid was named the greatest engi...
E. Bozovic G. Lellogg I. Mazin J. Sarrao W. K. Kwok
Multiband superconductivity in HoNi 2B 2C
HoNi 2B 2C single crystals prepared by the floating zone method were investigated by resistivity, magnetization, specific heat and point-contact measurements. The coexistence of superconductivity (SC) and antiferromagnetism (AFM) in HoNi 2B 2C is considered experimentally and theoretically for commensurate (C), incommensurate (IC) and metamagnetic magnetic structures within the multiband picture of Fermi surface sheets (FSS) obtained within full potential FPLO-LDA calculations. Special attention is paid to the admixture of Ho 5d states which mediate the pair breaking exchange between the Ho 4f derived local moments and the conduction electrons bearing the superconductivity. Within the paramagnetic and the uniform IC spiral phases, anisotropic multiband SC coexists with magnetism. Within the C-phase (below TN = 5.3 K) single band isotropic SC survives at a single FSS free of Ho 5d states in accord with isotropic standard WHH shaped upper critical fields Hc2( T). The superconducting energy gap obtained from point-contact data was found to disappear at a slightly higher temperature T? = 5.6 K which is also observed in specific heat measurements. Using the experimental values for the energy gap ?(0) and Hc2(0) at zero temperature, the characteristic phonon frequency, the electron-phonon coupling constant and the Fermi velocity of the residual superconducting phase were estimated from the standard isotropic single band model.
M³ller, Karl-Hartmut; Fuchs, G³nter; Drechsler, Stefan-Ludwig; Opahle, Ingo; Eschrig, Helmut; Schultz, Ludwig; Behr, G³nter; L÷ser, Wolfgang; Souptel, Dmitri; Wõlte, Andreas; Nenkov, Konstantin; Naidyuk, Yuri; Rosner, Helge
Effect of electron divergence in air gaps on the measurement of the energy of cascades in emulsion chambers
The effect of an increase in electron density in the vicinity of the cascade axis caused by an avalanche passing through the gap between lead filters of the emulsion chamber was investigated experimentally. Optical densities were measured in three X-ray films spaced at 400, 800 and 1200 micrometer from the filter surface having a thickness of 6 cascade units. The optical densities of blackening spots caused by electron photon cascades of 1 to 2, 2 to 7 and greater than 7 BeV energies were measured. The results prove the presence of a gap between the filter and the nuclear emulsion which results in the underestimation of energy by several tenths of a percent.
Apanasenko, A. V.; Baradzey, L. T.; Kanevskaya, Y. A.; Smorodin, Y. A.
Perfect self-similarity of energy spectra and gap-labeling properties in one-dimensional Fibonacci-class quasilattices
One-dimensional Fibonacci-class quasilattices are proposed and studied, which are constructed by the substitution rules B-->Bn-1 A, A-->Bn-1 AB. We have proved that this class of binary lattices is self-similar and also quasiperiodic. By the use of the renormalization-group technique, it has been proved that for all Fibonacci-class lattices the electronic energy spectra are perfect self-similar, and the branching rules of spectra are obtained. We analytically prove that each energy gap can be simply labeled by a characteristic integer, i.e., for the Fibonacci-class lattices there is a universal gap-labeling theorem [Phys. Rev. B 46, 9216 (1992)].
Fu, Xiujun; Liu, Youyan; Zhou, Peiqin; Sritrakool, Wichit
Micro superconducting magnetic energy storage (SMES) system for protection of critical industrial and military loads
A 6 MJ, 750 kVA Micro SMES system has been designed to protect critical loads against voltage sags and interruptions, as well as to provide continuous power conditioning. Life-cycle costs have been minimized through the use of energy efficient refrigeration units. Maintenance is simplified through the use of Line Replaceable Units (LRU). Availability is maximized through a design approach which allows the magnet to continue protecting the load even in the case of refrigeration degradation or total failure. Reliability is maximized by the use of proven commercial-off-the-shelf (COTS) items. The system provides ride-through capability for {approximately}9 seconds at a power level of 454 kW. The system comprises a niobium titanium superconducting magnet, permanent conduction cooled hybrid current leads, a low loss cryostat, a closed-loop refrigeration subsystem, an off-the-shelf uninterruptible power supply (UPS), a magnet interface unit to connect the magnet to the UPS, and an off-the-shelf monitoring unit providing both local and remote monitoring capability of system parameters.
Kalafala, A.K.; Bascunan, J.; Bell, D.D.; Blecher, L.; Murray, F.S.; Parizh, M.B.; Sampson, M.W.; Wilcox, R.E. [Intermagnetics General Corp., Lantham, NY (United States)] [Intermagnetics General Corp., Lantham, NY (United States)
30-MJ superconducting magnetic-energy-storage stabilizing system: an overview
The 30-MJ superconducting magnetic-energy-storage (SMES) system was devised as an alternate means to modulate the Bonneville Power Administration (BPA) Pacific AC Intertie, a part of the Western US Power System, to prevent undamped power oscillations at 0.35 Hz that were observed to be associated with high power transmission. The SMES system was installed at the BPA Tacoma Substation and successfully operated as an experimental device to initiate tests to determine power system dynamics, to investigate their variability, to assess system response to SMES modulation with a major variable load, and to use SMES to develop stability-control techniques. The system has been operated at frequencies of 0.1 to 1.0 Hz at power levels of +- 8.3 MW with a parallel modulation of the converter bridges and up to 9.5 MW reactive power together with +- 4.5 MW real power in constant VAR mode with buck-boost modulation of the bridges. The coil has been charged at a maximum rate of 11.8 MW. Operation of the SMES system is now under BPA jurisdiction, and all hardware has been transferred to BPA.
Roger, J.D.; Boenig, H.J.; Dean, J.W.; Schermer, R.I.; Annestrand, S.A.; Hauer, J.F.; Miller, B.L.
Superconducting magnetic energy storage (SMES) program. Progress report, January 1-December 31, 1984
The 30 MJ, 10 MW superconducting magnetic energy storage (SMES) system was devised to interact in the Western US Power System as an alternate means to damp unstable oscillations at 0.35 Hz on the Pacific HVAC Intertie. The SMES unit was installed at the Tacoma Substation of the Bonneville Power Administration (BPA). The operating limits of the 30 MJ SMES unit were established, and different means of controlling real and reactive power were tested. The unit can follow a sinusoidal power demand signal with an amplitude of up to 8.6 MW with the converter working in a 12 pulse mode. When the converter operates in the constant VAR mode, a time varying real power demand signal of up to 5 MW can be met. Experiments showed that the Pacific ac Intertie has current and reactive power variations of the same frequency as the modulating frequency of the SMES device. Endurance tests were run to assess the reliability of the SMES subsystems with a narrow band noise input, which is characteristic of the modulation signal for stabilizer operation. During the endurance tests, parameters of the ac power system were determined. Converter short circuit tests, load tests under various control conditions, dc breaker tests for coil current interruption, and converter failure mode tests were conducted. The experimental operation of the SMES system was concluded and the operation was terminated in early 1984.
Ultra-small metallic grains: effect of statistical fluctuations of the chemical potential on superconducting correlations and vice versa.
Superconducting correlations in an isolated metallic grain are governed by the interplay between two energy scales: the mean level spacing ? and the bulk pairing gap ?0, which are strongly influenced by the position of the chemical potential with respect to the closest single-electron level. In turn superconducting correlations affect the position of the chemical potential. Within the parity projected BCS model we investigate the probability distribution of the chemical potential in a superconducting grain with randomly distributed single-electron levels. Taking into account statistical fluctuations of the chemical potential due to the pairing interaction, we find that such fluctuations have a significant impact on the critical level spacing ?c at which the superconducting correlations cease: the critical ratio ?c/?0 at which superconductivity disappears is found to be increased. PMID:22718693
Croitoru, M D; Shanenko, A A; Kaun, C C; Peeters, F M
Ambipolar Charge Transport in Organic Field-Effect Transistors Based on Lead Phthalocyanine with Low Band Gap Energy
The organic semiconductor, lead phthalocyanine (PbPc) with a low band gap energy of 1.2 eV is demonstrated as an active material for high-performance ambipolar organic field-effect transistors (OFETs). For the ambipolar OFETs with Au source-drain electrodes, the field-effect electron mobility was calculated to be 8.3ū10-4 cm2 V-1 s-1, when the threshold voltage was 31 V. On the other hand, the
Takeshi Yasuda; Tetsuo Tsutsui
Scanning Josephson tunneling microscopy of single-crystal Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} with a conventional superconducting tip.
We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson I_{C}R_{N} product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local I_{C}R_{N} product and the local energy gap. PMID:18764282
Kimura, Hikari; Barber, R P; Ono, S; Ando, Yoichi; Dynes, R C
Scanning Josephson Tunneling Microscopy of Single Crystal Bi2Sr2CaCu2O8+delta with a Conventional Superconducting Tip
We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi2Sr2CaCu2O8+ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson ICRN product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local ICRN product and the local energy gap.
Kimura, H.; Barber Jr., R. P.; Ono, S.; Ando, Yoichi; Dynes, Robert C.
Superconducting Nuclear Particle Detector.
Work was undertaken to determine the feasibility of using thin superconducting films as nuclear particle detectors. The results of experiments show conclusively that such devices can be used to detect such radiation. The diffusion of energy from electrons...
D. E. Spiel R. W. Boom E. C. Crittenden
Large-bore, superconducting magnets for high-energy density propellant storage
A study has been conducted on the design of large-bore, superconducting solenoid magnets in an effort to determine how weight and cost scales with field and size. The fields considered ranged from 0.5 to 20 T and bore sizes from 3 to 10 m. The designs are based on light-weight, high-performance superconducting magnet designs using cable-in-conduit niobium-titanium and niobium-tin conductors.
M. S. Lubell; J. W. Lue; B. Palaszewski
Correlation between crystallite size¢optical gap energy and precursor molarities of ZnO thin films
We investigated the structural and optical properties of ZnO thin films as an n-type semiconductor. The films were deposited at different precursor molarities using an ultrasonic spray method. In this paper we focused our attention on a new approach describing a correlation between the crystallite size and optical gap energy with the precursor molarity of ZnO thin films. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along the c-axis. The maximum value of the crystallite size of the films is 63.99 nm obtained at 0.1 M. The films deposited with 0.1 M show lower absorption within the visible wavelength region. The optical gap energy increased from 3.08 to 3.37 eV with increasing precursor molarity of 0.05 to 0.1 M. The correlation between the structural and optical properties with the precursor molarity suggests that the crystallite size of the films is predominantly influenced by the band gap energy and the precursor molarity. The measurement of the crystallite size by the model proposed is equal to the experimental data. The minimum error value was estimated by Eq. (4) in the higher crystallinity.
Benramache, S.; Belahssen, O.; Guettaf, A.; Arif, A.
Experimental Indications of a BCS Behaviour in Superconducting Diamond
This special issue of physica status solidi which was guest-edited by Satoshi Koizumi (National Institute for Materials Science, Tsukuba, Japan), Christoph E. Nebel (Diamond Research Center, Tsukuba, Japan), and Milos Nesladek (CEA-LIST, Gif sur Yvette, France) presents 10 Review Articles covering different areas of CVD Diamond research.The cover picture was taken from the article by Sacķpķ et al. [1]. The authors present a scanning tunneling spectroscopy study of superconducting single-crystalline heavily boron-doped diamond providing an experimental evidence for BCS behaviour. When a perpendicular magnetic field is applied to a superconducting boron-doped diamond film, vortices penetrate the sample, each carrying one quantum flux. In their centre, the superconductivity is washed out on a length scale equal to the superconducting coherence length s. The figures show the electronic Density of States (DOS) measured with a scanning tunnelling microscope at 50 mK along a line crossing the centre of a such a vortex. Outside the vortex core which extends between the two arrows, the DOS presents a gap at the Fermi level (V = 0) and two coherence peaks characteristic of a superconducting DOS. The measured DOS inside the vortex core reveals in addition numerous localized resonances, at positions pointed out by the black arrows on the two-dimensional view. For clean superconductors, quasi-particles are expected to form localized states inside the vortex cores at energies close to the Fermi level. Here, although boron-doped diamond films are in the dirty limit, localized resonances are still visible but at non zero energies inside the superconducting gap.
Sacķpķ, B.; Chapelier, C.; Marcenat, C.; Kamarik, J.; Klein, T.; OmnĶs, F.; Bustarret, E.
Sacķpķ, B.; Chapelier, C.; Marcenat, C.; Kamarik, J.; Klein, T.; OmnĶs, F.; Bustarret, E.
Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata.
Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A&M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ▒0.1░, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ▒0.1░ during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase?Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata. PMID:24289392
Som, Sumit; Ghosh, Surajit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Roy, Suprakash
Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata
Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A&M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ▒0.1░, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ▒0.1░ during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.
Design and testing of a 13. 75-MW converter for a superconducting magnetic-energy-storage system
A 30 MJ superconducting magnetic energy storage system will be installed in 1982 in Tacoma, WA, to act as a transmission line stabilizer. Two 6 MVA transformers and a 5.5 kA, + 2.5 kV converter will connect the superconducting coil to the 13.8 kV bus and regulate the power flow between the coil and the three phase system. The design philosophy for the converter including its control and protection system is given in the paper. The converter has been tested with 10% overvoltage at no load, with 10% overcurrent at zero output voltage and with a watercooled resistive load of about 1 MW. These test results show that the converter will meet the expected full load operating conditions.
Boenig, H.J.; Turner, R.D.; Neft, C.L.; Sueker, K.H.
Design and construction of the main linac module for the superconducting energy recovery linac project at Cornell
Cornell University has been designing and building superconducting accelerators for various applications for more than 50 years. Currently, an energy-recovery linac (ERL) based synchrotron-light facility is proposed making use of the existing CESR facility. As part of the phase 1 R&D program funded by the NSF, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode - with individual HOM absorbers and one magnet/ BPM section. Pushing the limits, a high quality factor of the cavities (2?1010) and high beam currents (100 mA accelerated plus 100 mA decelerated) are targeted. We will present the design of the main linac cryo-module (MLC) being finalized recently, its cryogenic features and report on the status of the fabrication which started in late 2012.
Eichhorn, R.; Bullock, B.; He, Y.; Hoffstaetter, G.; Liepe, M.; O'Connell, T.; Quigley, P.; Sabol, D.; Sears, J.; Smith, E.; Veshcherevich, V.
Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A and M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9¢27 MHz with amplitude and phase stability of 100 ppm and ▒0.1░, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ▒0.1░ during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.
Som, Sumit; Ghosh, Surajit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Roy, Suprakash [Variable Energy Cyclotron Centre, Kolkata (India)] [Variable Energy Cyclotron Centre, Kolkata (India)
Far Infrared Studies of Superconducting V sub 3 Si, Nb sub 3 Ge and Nb. Final Report.
Far infrared spectroscopy between 10 and 250 cm exp -1 is an effective probe of superconductivity because typical gap and phonon energies lie in this region. Between 1979 and 1985, this DOE contract supported far infrared research in homogeneous high-T/su...
S. Perkowitz
Energy Gap and Averaged Inversion Symmetry of Tight-Binding Electrons on Generalized Honeycomb Lattice
We study the condition to open a finite gap in tight-binding electrons on an extended honeycomb lattice with the next-nearest-neighbor transfer integrals t2a, t2b, t2c, t2d, t2e, and t2f, where t2a, t2b, and t2c are transfer integrals between the sublattice A and t2d, t2e, and t2f are transfer integrals between the sublattice B. If the system has the inversion symmetry in this model, i.e., the sublattices A and B have the same on-site potential (?A=?B), the gap is zero. We find that although the finite gap is generally opened by inversion-symmetry breaking, the gap remains zero if the averaged inversion symmetry, which is defined as the sum of the transfer integrals and the on-site potentials of the sublattices are the same (t2a+t2b+t2c+?A=t2d+t2e+t2f+?B), is conserved.
Kishigi, Keita; Hanada, Hirotoshi; Hasegawa, Yasumasa
Crystalline color superconductivity
In any context in which color superconductivity arises in nature, it is likely to involve pairing between species of quarks with differing chemical potentials. For suitable values of the differences between chemical potentials, Cooper pairs with nonzero total momentum are favored, as was first realized by Larkin, Ovchinnikov, Fulde, and Ferrell (LOFF). Condensates of this sort spontaneously break translational and rotational invariance, leading to gaps which vary periodically in a crystalline pattern. Unlike the original LOFF state, these crystalline quark matter condensates include both spin-zero and spin-one Cooper pairs. We explore the range of parameters for which crystalline color superconductivity arises in the QCD phase diagram. If in some shell within the quark matter core of a neutron star (or within a strange quark star) the quark number densities are such that crystalline color superconductivity arises, rotational vortices may be pinned in this shell, making it a locus for glitch phenomena.
Alford, Mark; Bowers, Jeffrey A.; Rajagopal, Krishna
Evolution from a Nodeless Gap to dx2-y2-Wave in Underdoped La2-xSrxCuO4
Using angle-resolved photoemission spectroscopy (ARPES), it is revealed that the low-energy electronic excitation spectra of highly underdoped superconducting and nonsuperconducting La2-xSrxCuO4 cuprates are gapped along the entire underlying Fermi surface at low temperatures. We show how the gap function evolves to a dx2-y2 form with increasing temperature or doping, consistent with the vast majority of ARPES studies of cuprates. Our results provide essential information for uncovering the symmetry of the order parameter(s) in strongly underdoped cuprates, which is a prerequisite for understanding the pairing mechanism and how superconductivity emerges from a Mott insulator.
Razzoli, E.; Drachuck, G.; Keren, A.; Radovic, M.; Plumb, N. C.; Chang, J.; Huang, Y.-B.; Ding, H.; Mesot, J.; Shi, M.
Probing the superconductivity of PrPt4Ge12 through Ce substitution
We report measurements of electrical resistivity, magnetic susceptibility, specific heat, and thermoelectric power on the system Pr1-xCexPt4Ge12. Superconductivity is suppressed with increasing Ce concentration up to x =0.5, above which there is no evidence for superconductivity down to 1.1 K. The Sommerfeld coefficient ? increases with increasing x from ś48 mJ/mol K2 up to ś120 mJ/mol K2 at x = 0.5, indicating an increase in strength of electronic correlations. The temperature dependence of the specific heat at low temperatures evolves from roughly T3 for x = 0 to e-?/T behavior for x = 0.05 and above, suggesting a crossover from a nodal to a nodeless superconducting energy gap or a transition from multiband to single-band superconductivity. Fermi-liquid behavior is observed throughout the series in low-temperature magnetization, specific heat, and electrical resistivity measurements.
Huang, K.; Shu, L.; Lum, I. K.; White, B. D.; Janoschek, M.; Yazici, D.; Hamlin, J. J.; Zocco, D. A.; Ho, P.-C.; Baumbach, R. E.; Maple, M. B.
Coexistence of ferromagnetism and superconductivity
A comprehensive theory is developed that describes the coexistence of p-wave, spin-triplet superconductivity, and itinerant ferromagnetism. It is shown how to use field-theoretic techniques to derive both conventional strong-coupling theory, and analogous gap equations for superconductivity induced by magnetic fluctuations. It is then shown and discussed in detail that the magnetic fluctuations are generically stronger on the ferromagnetic side of the magnetic phase boundary, which substantially enhances the superconducting critical temperature in the ferromagnetic phase over that in the paramagnetic one. The resulting phase diagram is compared with the experimental observations in UGe2 and ZrZn2.
Kirkpatrick, T. R.; Belitz, D.
Buffer layer induced band gap and surface low energy optical phonon scattering in epitaxial graphene on SiC(0001)
The temperature dependent electrical properties of epitaxial graphene grown on Si-face and C-face SiC substrates were investigated by Hall measurements, respectively. Quasi-free-standing epitaxial graphene by H2 intercalation was adopted as the control. Due to a ~200 meV band gap, the electrical conductivities of graphene on Si-face SiC showed a great increase at temperatures above 350 K compared to the other two. The opened band gap was found attributed to the existent buffer layer. The fitting results of Hall mobility indicates that the buffer layer also limits the carrier transportation of graphene grown on Si-face SiC, as it introduced low energy optical phonon scattering to its epilayer.
Yu, C.; Li, J.; Liu, Q. B.; Dun, S. B.; He, Z. Z.; Zhang, X. W.; Cai, S. J.; Feng, Z. H.
Electron Energy Loss Spectroscopy Measurement of the Optical Gaps on Individual Boron Nitride Single-Walled and Multiwalled Nanotubes
Spatially resolved electron energy loss spectroscopy experiments have been performed in an electron microscope on several individual boron nitride (BN) single-, double-, and triple-walled nanotubes, whose diameters and number of shells have been carefully measured. In the low-loss region (from 2 to 50 eV) the spectra have been analyzed within the framework of the continuum dielectric theory, leading to the conclusion of a weak influence of out-of-plane contribution to the dielectric response of the tubes. The gap has been measured to be independent of the nanotubes geometry, and close to the in-plane gap value of hexagonal BN (5.8▒0.2eV).
Arenal, R.; Stķphan, O.; Kociak, M.; Taverna, D.; Loiseau, A.; Colliex, C.
Electron energy loss spectroscopy measurement of the optical gaps on individual boron nitride single-walled and multiwalled nanotubes.
Spatially resolved electron energy loss spectroscopy experiments have been performed in an electron microscope on several individual boron nitride (BN) single-, double-, and triple-walled nanotubes, whose diameters and number of shells have been carefully measured. In the low-loss region (from 2 to 50 eV) the spectra have been analyzed within the framework of the continuum dielectric theory, leading to the conclusion of a weak influence of out-of-plane contribution to the dielectric response of the tubes. The gap has been measured to be independent of the nanotubes geometry, and close to the in-plane gap value of hexagonal BN (5.8+/-0.2 eV). PMID:16197110
Arenal, R; Stķphan, O; Kociak, M; Taverna, D; Loiseau, A; Colliex, C
The role of gap states in the energy level alignment at the organic-organic heterojunction interfaces.
The interface properties of organic-organic heterojunctions (OOHs), such as interface energy level alignment (ELA), interfacial charge transfer, interface nanostructuring, molecular orientation and so on, play an essential role in determining the device performance for some technologically important organic electronic devices, encompassing organic solar cells, bipolar organic field-effect-transistors, and organic light-emitting-diodes. The aim of this article is to provide a balanced assessment on the understanding of the ELA at the small-molecule based OOH interfaces with well-defined molecular orientation, with particular emphasis on the role of gap states in organic thin films. A generalized picture of gap states determined ELA at the OOH interfaces is provided and their implications in relevant organic electronic devices have been discussed. PMID:22903473
Zhong, Shu; Zhong, Jian Qiang; Mao, Hong Ying; Zhang, Jia Lin; Lin, Jia Dan; Chen, Wei
Superconducting Transducer.
The patent application describes a high power density, low frequency superconducting transducer which includes an electro-dynamic drive wherein a superconducting magnet provides the primary driving force for two AC-driven copper coils. Each of the copper ...
M. G. Karamargin
Superconductive wire
A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity.
Korzekwa, David A. (Los Alamos, NM); Bingert, John F. (Jemez Springs, NM); Peterson, Dean E. (Los Alamos, NM); Sheinberg, Haskell (Santa Fe, NM)
A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity. 2 figs.
Korzekwa, D.A.; Bingert, J.F.; Peterson, D.E.; Sheinberg, H.
Superconductivity and information exchange
The author was invited to visit several institutions in Europe for the purposes of collaboration, information exchange, and presentation of seminars. Extensive exchanges of information regarding the current state of the field in high-temperature superconductivity took place. Five seminars on the recent work of Klemm and Liu on interlayer pairing were given, and the response was very favorable. A new collaboration on the role of gap anisotropy on the physical properties of high-temperature superconductors was begun.
Klemm, R. A.
Electronic Characterization of Defects in Narrow Gap Semiconductors-Comparison of Electronic Energy Levels and Formation Energies in Mercury Cadmium Telluride, Mercury Zinc Telluride, and Mercury Zinc Selenide
We have used a Green's function technique to calculate the energy levels and formation energy of deep defects in the narrow gap semiconductors mercury cadmium telluride (MCT), mercury zinc telluride (MZT) and mercury zinc selenide (MZS). The formation energy is calculated from the difference between the total energy with an impurity cluster and the total energy for the perfect crystal. Substitutional (including antisite), interstitial (self and foreign), and vacancy deep defects are considered. Relaxation effects are calculated (with molecular dynamics). By use of a pseudopotential, we generalize the ideal vacancy model so as to be able to consider relaxation for vacancies. Different charge states are considered and the charged state energy shift (as computed by a modified Haldane-Anderson model) can be twice that due to relaxation. Different charged states for vacancies were not calculated to have much effect on the formation energy. For all cases we find deep defects in the energy gap only for cation site s-like orbitals or anion site p-like orbitals, and for the substitutional case only the latter are appreciably effected by relaxation. For most cases for MCT, MZT, MZS, we consider x (the concentration of Cd or Zn) in the range appropriate for a band gap of 0.1 eV. For defect energy levels, the absolute accuracy of our results is limited, but the precision is good, and hence chemical trends are accurately predicted. For the same reason, defect formation energies are more accurately predicted than energy level position. We attempt, in Appendix B, to calculate vacancy formation energies using relatively simple chemical bonding ideas due to Harrison. However, these results are only marginally accurate for estimating vacancy binding energies. Appendix C lists all written reports and publications produced for the grant. We include abstracts and a complete paper that summarizes our work which is not yet available.
Patterson, James D.
Design features of high-intensity medium-energy superconducting heavy-ion Linac.
The proposed Rare Isotope Accelerator (RIA) requires the construction of a cw 1.4 GV superconducting (SC) linac that is capable of producing 400 kW beams of all ions from protons at 900 MeV to uranium at 400 MeV/u. The design of such a linac was outlined at the previous Linac conference. This linac will accelerate multiple-charge-states (multi-q) of the heaviest ion beams, for which the beam current is limited by ion-source performance. The linac consists of two different types of accelerating and focusing lattice: for uranium below {approx}85 MeV/u the focusing is provided by SC solenoids installed in cryostats with the SC resonators while in the high-beta section the focusing elements are located outside of the cryostats. A detailed design has been developed for the focusing-accelerating lattice of the linac. Beam dynamics studies have been performed with the goal of optimization of the linac structure in order to reduce a possible effective emittance growth of the multi-q uranium beam. A wide tuning range of the accelerating and focusing fields is required for acceleration of the variety of ions with different charge-to-mass ratios to the highest possible energy in single charge state mode. The focusing must be retuned for different ion masses to avoid resonance coupling between the transverse and longitudinal motions. Any visible impact of this coupling on the formation of beam halo must be avoided due to the high beam power.
Ostroumov, P. N.
Potential for precision measurement of low-energy antiprotons with GAPS for dark matter and primordial black hole physics
The general antiparticle spectrometer (GAPS) experiment is a proposed indirect dark matter search focusing on antiparticles produced by WIMP (weakly interacting massive particle) annihilation and decay in the Galactic halo. In addition to the very powerful search channel provided by antideuterons (Donato et al., 2000, 2008) [1,2], (Vittino et al.) [3], (Fornengo, 2013) [4], GAPS has a strong capability to measure low-energy antiprotons (0.07?E?0.25 GeV) as dark matter signatures. This is an especially effective means for probing light dark matter, whose existence has been hinted at in the direct dark matter searches, including the recent result from the CDMS-II experiment (Agnese, 2013) [5]. While severely constrained by LUX and other direct dark matter searches (Akerib et al.) [6], light dark matter candidates are still viable in an isospin-violating dark matter scenario and halo-independent analysis (Del Nobile et al.) [7,8]. Along with the excellent antideuteron sensitivity, GAPS will be able to detect an order of magnitude more low-energy antiprotons, compared to BESS (Abe et al., 2012) [9], (Orito et al., 2000) [10], PAMELA (Adriani et al., 2010) [11] and AMS-02 (Casaus, 2009) [12], providing a precision measurement of low-energy antiproton flux and a unique channel for probing light dark matter models. Additionally, dark matter signatures from gravitinos and Kaluza-Klein right-handed neutrinos as well as evidence of primordial black hole evaporation can be observed through low-energy antiproton search.
Aramaki, T.; Boggs, S. E.; von Doetinchem, P.; Fuke, H.; Hailey, C. J.; Mognet, S. A. I.; Ong, R. A.; Perez, K.; Zweerink, J.
Effect of topological defects and Coulomb charge on the low energy quantum dynamics of gapped graphene
We study the combined effect of a conical topological defect and a Coulomb charge impurity on the dynamics of Dirac fermions in gapped graphene. Beyond a certain strength of the Coulomb charge, quantum instability sets in, which demarcates the boundary between sub- and supercritical values of the charge. In the subcritical regime, for certain values of the system parameters, the allowed boundary conditions in a gapped graphene cone can be classified in terms of a single real parameter. We show that the observables such as local density of states, scattering phase shifts and the bound state spectra are sensitive to the value of this real parameter, which is interesting from an empirical point of view. For a supercritical Coulomb charge, we analyze the system with a regularized potential as well as with a zigzag boundary condition and find the effect of the sample topology on the observable features of the system.
Chakraborty, Baishali; Gupta, Kumar S.; Sen, Siddhartha
Electronic absorption spectra and energy gap studies of Er3+ ions in different chlorophosphate glasses.
Spectroscopic properties of Er3+ ions in different chlorophosphate glasses 50P2O5-30Na2HPO4-19.8RCl (R = Li, Na, K, Ca and Pb) are studied. The direct and indirect optical band gaps (Eopt) and the various spectroscopic parameters (E1, E2, E3, and zeta4f and alpha) are reported. The oscillator strengths of the transitions in the absorption spectrum are parameterized in terms of three Judd-Ofelt intensity parameters (omega2, omega4 and omega6). These intensity parameters are used to predict the transition probabilities (A), radiative lifetimes (tauR), branching ratios (beta) and integrated cross sections (sigma) for stimulated emission. Attention has been paid to the trend of the intensity parameters over hypersensitive transitions and optical band gaps. The lifetimes and branching ratios of certain transitions are compared with other glass matrices. PMID:12166752
Ratnakaram, Y C; Reddy, A Viswanadha; Chakradhar, R P Sreekanth
BSCCO superconductors : hole-like fermi surface and doping dependence of the gap function.
We use the gradient of the energy-integrated angle resolved photoemission (ARPES) intensity in order to define precisely the Fermi surface (FS) in BSCCO superconductors. We show that, independent of the photon energy, the FS is a hole barrel centered at ({pi},{pi}), Then, the superconducting gap along the FS is precisely determined from ARPES measurements on over-doped and underdoped samples of Bi2212. As the doping decreases, the maximum gap increases, but the slope of the gap near the nodes decreases. Though consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple cos(k{sub x})-cos(k{sub y}) form. A comparison of our ARPES results with available penetration depth data indicates that the renormalization of the linear T suppression of the superfluid density at low temperatures due to quasiparticle excitations around the d-wave nodes is large and doping dependent.
Campuzano, J. C.; Ding, H.; Fretwell, H. M.; Kadowaki, K.; Kaminski, A.; Mesot, J.; Mochiku, T.; Norman, M. R.; Paramekanti, A.; Randeria, M.; Sato, T.; Takahashi, T.; Takeuchi, T.; Yokoya, T.
Odd-parity superconductivity in Weyl semimetals
Unconventional superconducting states of matter are realized in the presence of strong spin-orbit coupling. In particular, nondegenerate bands can support odd-parity superconductivity with rich topological content. Here we study whether this is the case for Weyl semimetals. These are systems whose low-energy sector, in the absence of interactions, is described by linearly dispersing chiral fermions in three dimensions. The energy spectrum has nodes at an even number of points in the Brillouin zone. Consequently both intranodal finite momentum pairing and internodal BCS superconductivity are allowed. For local attractive interaction the finite momentum pairing state with chiral p-wave symmetry is found to be most favorable at finite chemical potential. The state is an analog of the superfluid 3He A phase, with Cooper pairs having finite center-of-mass momentum. For chemical potential at the node the state is preempted by a fully gapped charge density wave. For nonlocal attraction the BCS state wins out for all values of the chemical potential.
Wei, Huazhou; Chao, Sung-Po; Aji, Vivek
Unconventional superconductivity in Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2} from inelastic neutron scattering.
A new family of superconductors containing layers of iron arsenide has attracted considerable interest because of their high transition temperatures (T{sub c}), some of which are >50 K, and because of similarities with the high-T{sub c} copper oxide superconductors. In both the iron arsenides and the copper oxides, superconductivity arises when an antiferromagnetically ordered phase has been suppressed by chemical doping. A universal feature of the copper oxide superconductors is the existence of a resonant magnetic excitation, localized in both energy and wavevector, within the superconducting phase. This resonance, which has also been observed in several heavy-fermion superconductors, is predicted to occur when the sign of the superconducting energy gap takes opposite values on different parts of the Fermi surface, an unusual gap symmetry which implies that the electron pairing interaction is repulsive at short range. Angle-resolved photoelectron spectroscopy shows no evidence of gap anisotropy in the iron arsenides, but such measurements are insensitive to the phase of the gap on separate parts of the Fermi surface. Here we report inelastic neutron scattering observations of a magnetic resonance below T{sub c} in Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2}, a phase-sensitive measurement demonstrating that the superconducting energy gap has unconventional symmetry in the iron arsenide superconductors.
Christianson, A. D.; Goremychkin, E. A.; Osborn, R.; Rosenkranz, S.; Lumsden, M. D.; Malliakas, C. D.; Todorov, I. S.; Claus, H.; Chung, D. Y.; Kanatzidis, M. G.; Bewley, R. I.; Guidi, T.; ORNL; Rutherford Appleton Lab.; Northwestern Univ.
Restoration of the derivative discontinuity in Kohn-Sham density functional theory: an efficient scheme for energy gap correction.
From the perspective of perturbation theory, we propose a systematic procedure for the evaluation of the derivative discontinuity (DD) of the exchange-correlation energy functional in Kohn-Sham (KS) density functional theory, wherein the exact DD can in principle be obtained by summing up all the perturbation corrections to infinite order. Truncation of the perturbation series at low order yields an efficient scheme for obtaining the approximate DD. While the zeroth-order theory yields a vanishing DD, the first-order correction to the DD can be expressed as an explicit universal functional of the ground-state density and the KS lowest unoccupied molecular orbital density, allowing the direct evaluation of the DD in the standard KS method without extra computational cost. The fundamental gap can be predicted by adding the estimated DD to the KS gap. This scheme is shown to be accurate in the prediction of the fundamental gaps for a wide variety of atoms and molecules. PMID:23373919
Progress in superconducting metamaterials
We review progress in the development and applications of superconducting metamaterials. The review is organized in terms of several distinct advantages and unique properties brought to the metamaterials field by superconductivity. These include the low-loss nature of the meta-atoms, their compact structure, their extraordinary degree of nonlinearity and tunability, magnetic flux quantization and the Josephson effect, quantum effects in which photons interact with quantized energy levels in the meta-atom, as well as strong diamagnetism.
Jung, Philipp; Ustinov, Alexey V.; Anlage, Steven M.
Photoinduced Melting of Superconductivity in the High-Tc Superconductor La2?xSrxCuO4 Probed by Time-resolved Optical and Terahertz Techniques
The dynamics of depletion and recovery of a superconducting state in La{sub 2-x}Sr{sub x}CuO{sub 4} thin films is investigated utilizing optical pump-probe and optical pump-THz-probe techniques as a function of temperature and excitation fluence. The absorbed energy density required to suppress superconductivity is found to be about eight times higher than the thermodynamically determined condensation energy density and nearly temperature independent between 4 and 25 K. These findings indicate that, during the time when the superconducting state suppression takes place ({approx}0.7 ps), a large part (nearly 90%) of the energy is transferred to the phonons with energy lower than twice the maximum value of the superconducting gap and only 10% is spent on Cooper pair breaking.
Logvenov, G.; Beyer, M.; Staedter, D.; Beck, M.; Schaefer, H.; Kabanov, V.V.; Bozovic, I.; Koren, G.; Demsar, J.
Bound states in gapped graphene with impurities: Effective low-energy description of short-range interactions
We obtain a bound-state spectrum of low-energy excitations near the Fermi points of gapped graphene in the presence of a charge impurity. The effects of possible short-range interactions induced by the impurity are modeled by suitable boundary conditions. The spectrum in the subcritical region of the effective Coulomb coupling is labeled by a parameter which characterizes the boundary conditions and determines the inequivalent quantizations of the system. In the supercritical region we obtain a renormalization-group flow for the effective Coulomb coupling.
Gupta, Kumar S.; Sen, Siddhartha [Theory Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700064 (India); School of Mathematical Sciences, UCD, Belfield, Dublin 4, Ireland and Department of Theoretical Physics, Indian Association for the Cultivation of Science, Calcutta 700032 (India)
Electron excitations in solid C[sub 60]: Energy gap, band dispersions, and effects of orientational disorder
Electron excitation energies and photoemission spectra in undoped, solid C[sub 60] are calculated using a quasiparticle approach. The effects of orientational disorder and electron correlations are studied. We find a band gap of 2.15 eV, in good agreement with experiment, and [similar to]1 eV widths for the highest-occupied-molecular-orbital (HOMO) and lowest-unoccupied-molecular-orbital (LUMO) bands. Calculated angle-resolved, inverse photoemission spectra for the LUMO bands show very little angular dependence, explaining recent experimental work on epitaxial thin films. The present results suggest that undoped, solid C[sub 60] is a standard band insulator.
Shirley, E.L.; Louie, S.G. (Department of Physics, University of California, Berkeley, California 94720 (United States) Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States))
Magnetic-field dependence of energy levels of superconducting nano-scale mettalic grains with strong spin-orbit scattering
We study the Zeeman splitting of discrete energy levels of superconducting nano-scale metallic grains whose single-electron dynamics is chaotic [1]. In the absence of spin-orbit scattering the Zeeman splitting of a single-electron level is trivial; it is the same for all levels and linear in magnetic field. Spin-orbit coupling suppresses this splitting, induces level-to-level fluctuations and non-linear corrections to the energies. We investigate the combined effect of pairing correlations, which lead to superconductivity in the bulk limit, and spin-orbit scattering on the many-electron energy levels in a weak magnetic field. In particular, we focus our studies on the linear (g-factor) and quadratic (zero-field level curvature) corrections and their mesoscopic fluctuations. The single-electron part of the Hamiltonian follows the statistics of the Gaussian symplectic ensemble of random matrix theory, which is applicable in the limit of strong spin-orbit scattering and a large dimensionless Thouless conductance. The interaction is given by a BCS-like pairing term and the magnetic field coupling is described by a Zeeman term. [1] K. Nesterov and Y. Alhassid, to be published.
Nesterov, Konstantin; Alhassid, Yoram
Partially gapped Fermi surface in the heavy-electron superconductor URu2Si2
Transport, thermal, and magnetic data for the heavy electron system URu2Si2 indicate that a charge- or spin-density-wave transition opens an energy gap of ~11 meV over a portion of the Fermi surface below T0~=17.5 K and demonstrate that bulk superconductivity occurs below Tc~=1.5 K. The pressure dependences of T0 and Tc support this interpretation. The unusually large initial slope of
M. B. Maple; J. W. Chen; Y. Dalichaouch; T. Kohara; C. Rossel; M. S. Torikachvili; M. W. McElfresh; J. D. Thompson
Inter-Layer Superconducting Pairing Induced c-axis Nodal Lines in Iron-based Superconductors
A layered superconductor with a full pairing energy gap can be driven into a nodal superconducting (SC) state by inter-layer pairing when the SC state becomes more quasi-3D. We propose that this mechanism is responsible for the observed nodal behavior in a class of iron-based SCs. We show that the intra- and inter-layer pairings generally compete and the gap nodes develop on one of the hole Fermi surface pockets as they become larger in the iron-pnictides. Our results provide an explanation of the c-axis gap modulations and gap nodes observed by angle resolved photo emission spectroscopy. In addition, we predict that an anti-correlated c-axis gap modulations on the hole and electron pockets should be observable in the s▒-wave pairing state.
Setty, Chandan; Su, Yuehua; Wang, Ziqiang; Hu, Jiangping
Spatial correlation between impurity states and energy gap distribution in Bi2Sr2Ca(Cu1-xZnx)2 O8+?(x = 0.02)
We have performed scanning tunneling spectroscopy (STS) measurements on slightly over doped Bi2Sr2Ca(Cu1-xZnx)2O8+?(x = 0.02) to investigate spatial correlation between the impurity stats and the local gap value. In addition to several impurity states, the spatial variation of energy gap has been observed. The gap values are spatially distributed from 20 meV to 55 meV with the length scale of about 5 nm. The impurity states appear only in the regions whose gap values are less than 50 meV. Furthermore, the number of Zn impurity states estimated from STS results is slightly less than that of doped Zn atoms estimated by inductively-coupled-plasma-mass-spectroscopy. Our results insist that there exist the impurity sites without the resonant states and those impurities are located on the region with the gap value of more than 50 meV.
Machida, Tadashi; Gaifullin, Marat B.; Mochiku, Takashi; Kato, Takuya; Sakata, Hideaki; Hirata, Kazuto
s- AND d-WAVE SYMMETRIES IN NONADIABATIC THEORY OF SUPERCONDUCTIVITY
High-Tc superconductors have Fermi energies EF much smaller than conventional metals comparable to phonon frequencies. In such a situation nonadiabatic effects are important. A generalization of Eliashberg theory in the nonadiabatic regime has previously been shown to reproduce some anomalous features of the high-Tc superconductors as for instance the enhancement of Tc or the isotopic effects on Tc and m*. In this contribution we address the issue of the symmetry of the gap in the context of nonadiabatic superconductivity. We show that vertex corrections have a momentum structure which favours d-wave superconductivity when forward scattering is predominant. An additional increase of Tc is also found.
Paci, Paola; Grimaldi, Claudio; Pietronero, Luciano; Cappelluti, Emmanuele
Coexistence of antiferromagnetism and d+id superconducting correlations in the graphene bilayer
We discuss the t-J-U model on a honeycomb monolayer that has the same low-energy description of the kinetic term as the graphene bilayer, and in particular study coexistence of antiferromagnetism and superconducting correlations that originate from Cooper pairs without phase coherence. We show that the model is relevant for the description of the graphene bilayer and that the presence of the d+id superconducting correlations with antiferromagnetism can lead to quadratic dependence in small magnetic fields of the gap of the effective monolayer consistent with the transport measurements of Velasco on the graphene bilayer.
Milovanovi?, M. V.; Predin, S.
Anomalous Energy Gaps of the Odd Denominator Fractional Quantum Hall States in Different Spin Branches of the Second Landau Level
The nature of the fractional quantum Hall states forming in the second Landau level, including those with odd denominator Landau level filling factors, remain unknown. Conjectures of nonconventional origins have lead to the investigation of several odd denominator states in the lower spin branch of the second Landau level, such as the ones at ?=2+1/3 and 2+2/3. We report first measurements of the energy gaps in the upper spin branch of the second Landau level at ?=3+1/3, 3+2/3, 3+1/5 and 3+4/5. A comparison of the energy gaps of these states to those of their counterparts in the lower spin branch reveals a surprising reversal in the relative magnitudes of the states at partial filling factors 1/3 and 1/5. We explore possible explanations of this unusual observation. The work at Purdue was supported by the DOE BES contract no. DE-SC0006671. K.K. West and L.N. Pfeiffer acknowledge the support of the Princeton NSF-MRSEC and the Moore Foundation.
Kleinbaum, Ethan; Kumar, Ashwani; Manfra, Michael; Pfeiffer, Loren; West, Ken; Csathy, Gabor
Influence of current re-distribution on minimum quench energy of superconducting triplex cable against local disturbance
Stability of multi-strand superconducting cable against local disturbances has been studied experimentally and theoretically. Quench experiments have been made with a superconducting triplex cable made of chrome-plated strands. A heat pulse is applied to a short part of one strand, and the minimum quench energy (MQE) against that local disturbance and the temporal evolution of the strand current during the quench or recovery process are measured. When the transport current divided by the critical current ( It/ Ic) is large, the MQE against a local disturbance almost equals the MQE of the single strand. When the overall It/ Ic is less than 0.4, the MQE against a local disturbance is much larger than the MQE of the single strand. In this small It/ Ic region, when a heat pulse whose energy is slightly less than the MQE is applied, current re-distribution is observed during the recovery process. Numerical simulations of the quench or recovery process have been made with a computer code named MST. The dependence of the calculated MQE on the It/ Ic qualitatively agrees with the experimental result. The numerical and experimental results prove that the stability against local disturbances is improved by the current re-distribution when the It/ Ic is less than some threshold value. This threshold appears to be influenced by the contact thermal conductance between strands.
Amemiya, N.; Yonekawa, H.; Ogitsu, T.; Kobayashi, E.; Sasaki, K.; Ohuchi, N.; Tsuchiya, K.; Miyashita, K.
Superconducting thermoelectric generator
An apparatus and method for producing electricity from heat. The present invention is a thermoelectric generator that uses materials with substantially no electrical resistance, often called superconductors, to efficiently convert heat into electrical energy without resistive losses. Preferably, an array of superconducting elements is encased within a second material with a high thermal conductivity. The second material is preferably a semiconductor. Alternatively, the superconducting material can be doped on a base semiconducting material, or the superconducting material and the semiconducting material can exist as alternating, interleaved layers of waferlike materials. A temperature gradient imposed across the boundary of the two materials establishes an electrical potential related to the magnitude of the temperature gradient. The superconducting material carries the resulting electrical current at zero resistivity, thereby eliminating resistive losses. The elimination of resistive losses significantly increases the conversion efficiency of the thermoelectric device.
Metzger, John D. (Eaton's Neck, NY); El-Genk, Mohamed S. (Albuquerque, NM)
An apparatus and method for producing electricity from heat is disclosed. The present invention is a thermoelectric generator that uses materials with substantially no electrical resistance, often called superconductors, to efficiently convert heat into electrical energy without resistive losses. Preferably, an array of superconducting elements is encased within a second material with a high thermal conductivity. The second material is preferably a semiconductor. Alternatively, the superconducting material can be doped on a base semiconducting material, or the superconducting material and the semiconducting material can exist as alternating, interleaved layers of waferlike materials. A temperature gradient imposed across the boundary of the two materials establishes an electrical potential related to the magnitude of the temperature gradient. The superconducting material carries the resulting electrical current at zero resistivity, thereby eliminating resistive losses. The elimination of resistive losses significantly increases the conversion efficiency of the thermoelectric device. 4 figs.
Metzger, J.D.; El-Genk, M.S.
Superconducting Cable
In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on th