# M. Potemski

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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## Publications (347)1043.39 Total impact

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##### Article: Quadexciton cascade and fine structure splitting of the triexciton in a single quantum dot
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ABSTRACT: We report the properties of emission lines associated with the cascaded recombination of a quadexciton in single GaAlAs/AlAs quantum dots, studied by means of polarization-resolved photoluminescence and single-photon correlation experiments. It is found that photons which are emitted in a double-step 4X-3X process preserve their linear polarization, similarly to the case of conserved polarization of correlated photons in the 2X-X cascade. In contrast, an emission of either co-linear or cross-linear pairs of photons is observed for the 3X-2X cascade. Each emission line associated with the quadexciton cascade shows doublet structure in the polarization-resolved photoluminescence experiment. The maximum splitting is seen when the polarization axis is chosen along and perpendicular to the [110] crystallographic direction. This effect is ascribed to the fine structure splitting of the exciton and triexciton states in the presence of an anisotropic confining potential of ae dot. We also show that the splitting in the triexciton state surpasses that in the exciton state by a factor up to eight and their ratio scales with the energy distance between the 3X and X emission lines, thus, very likely, with a lateral size and/or a composition of the dot.
• ##### Article: SU(4) symmetry breaking revealed by magneto-optical spectroscopy in epitaxial graphene
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ABSTRACT: Refined infrared magnetotransmission experiments have been performed in magnetic fields B up to 35 T on a series of multilayer epitaxial graphene samples. Following the main optical transition involving the n=0 Landau level (LL), we observe a new absorption transition increasing in intensity with magnetic fields B>26 T. Our analysis shows that this is a signature of the breaking of the SU(4) symmetry of the n=0 LL. Using a quantitative model, we show that the only symmetry-breaking scheme consistent with our experiments is a charge density wave (CDW).
Physical Review B 06/2015; 91(23). DOI:10.1103/PhysRevB.91.235122 · 3.74 Impact Factor
• ##### Article: Multiple magneto-phonon resonances in graphene
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ABSTRACT: Our low-temperature magneto-Raman scattering measurements performed on graphene-like locations on the surface of bulk graphite reveal a new series of magneto-phonon resonances involving both K-point and Gamma-point phonons. In particular, we observe for the first time the resonant splitting of three crossing excitation branches. We give a detailed theoretical analysis of these new resonances. Our results highlight the role of combined excitations and the importance of multi-phonon processes (from both K and Gamma points) for the relaxation of hot carriers in graphene.
• ##### Article: Magneto-resistance quantum oscillations in a magnetic two-dimensional electron gas
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ABSTRACT: Magneto-transport measurements of Shubnikov-de Haas (SdH) oscillations have been performed on two-dimensional electron gases (2DEGs) confined in CdTe and CdMnTe quantum wells. The quantum oscillations in CdMnTe, where the 2DEG interacts with magnetic Mn ions, can be described by incorporating the electron-Mn exchange interaction into the traditional Lifshitz-Kosevich formalism. The modified spin splitting leads to characteristic beating pattern in the SdH oscillations, the study of which indicates the formation of Mn clusters resulting in direct anti-ferromagnetic Mn-Mn interaction. The Landau level broadening in this system shows a peculiar decrease with increasing temperature, which could be related to statistical fluctuations of the Mn concentration.
Physical Review B 06/2015; 92(8). DOI:10.1103/PhysRevB.92.085304 · 3.74 Impact Factor
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##### Article: Magneto-Optics of Massive Dirac Fermions in Bulk Bi 2 Se 3
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ABSTRACT: We report on magneto-optical studies of Bi2Se3, a representative member of the 3D topological insulator family. Its electronic states in bulk are shown to be well described by a simple Dirac-type Hamiltonian for massive particles with only two parameters: the fundamental bandgap and the band velocity. In a magnetic field, this model implies a unique property - spin splitting equal to twice the cyclotron energy: Es = 2Ec. This explains the extensive magneto-transport studies concluding a fortuitous degeneracy of the spin and orbital split Landau levels in this material. The Es = 2Ec match differentiates the massive Dirac electrons in bulk Bi2Se3 from those in quantum electrodynamics, for which Es = Ec always holds.
Physical Review Letters 04/2015; 114(18). DOI:10.1103/PhysRevLett.114.186401 · 7.51 Impact Factor
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##### Article: Indirect-to-Direct Band Gap Crossover in Few-Layer MoTe 2
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ABSTRACT: We study the evolution of the band-gap structure in few-layer MoTe2 crystals, by means of low-temperature micro-reflectance (MR) and temperature-dependent photoluminescence (PL) measurements. The analysis of the measurements indicate that -in complete analogy with other semiconducting transition metal dichalchogenides (TMDs)- the dominant PL emission peaks originate from direct transitions associated to recombination of excitons and trions. When we follow the evolution of the PL intensity as a function of layer thickness, however, we observe that MoTe2 behaves differently from other semiconducting TMDs investigated earlier. Specifically, the exciton PL yield (integrated PL intensity) is identical for mono and bilayer, decreases slightly for trilayer and it is significantly lower in the tetralayer. The analysis of this behavior and of all our experimental observations is fully consistent with mono and bilayer MoTe2 being direct band-gap semiconductors, with tetralayer MoTe2 being an indirect gap semiconductor, and with trilayers having nearly identical direct and indirect gaps. This conclusion is different from the one reached for other recently investigated semiconducting transition metal dichalcogenides, for which monolayers are found to be direct band-gap semiconductors, and thicker layers have indirect band gaps that are significantly smaller -by hundreds of meV- than the direct gap. We discuss the relevance of our findings for experiments of fundamental interest and possible future device applications.
Nano Letters 03/2015; 15(4). DOI:10.1021/nl5045007 · 13.59 Impact Factor
• ##### Article: Infrared magneto-spectroscopy of two-dimensional and three-dimensional massless fermions: A comparison
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ABSTRACT: Here, we report on a magneto-optical study of two distinct systems hosting massless fermions—two-dimensional graphene and three-dimensional HgCdTe tuned to the zero band gap condition at the point of the semiconductor-to-semimetal topological transition. Both materials exhibit, in the quantum regime, a fairly rich magneto-optical response, which is composed from a series of intra- and interband inter-Landau level resonances with for massless fermions typical B dependence. The impact of the system&apos;s dimensionality and of the strength of the spin-orbit interaction on the optical response is also discussed.
Journal of Applied Physics 03/2015; 117(11):112803. DOI:10.1063/1.4913828 · 2.19 Impact Factor
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##### Article: Excitonic resonances in thin films of WSe2: From monolayer to bulk material
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ABSTRACT: We present optical spectroscopy (photoluminescence and reflectance) studies of thin layers of the transition metal dichalcogenide WSe2, with thickness ranging from mono- to tetra-layer and in the bulk limit. The investigated spectra show the evolution of excitonic resonances as a function of layer thickness, due to changes in the band structure and, importantly, due to modifications of the strength of Coulomb interaction as well. The observed temperature-activated energy shift and broadening of the fundamental direct exciton are well accounted for by standard formalisms used for conventional semiconductors. A large increase of the photoluminescence yield with temperature is observed in WSe2 monolayer, indicating the existence of competing radiative channels. The observation of absorption-type resonances due to both neutral and charged excitons in WSe2 monolayer is reported and the effect of the transfer of oscillator strength from charged to neutral exciton upon increase of temperature is demonstrated.
Nanoscale 03/2015; 7(23). DOI:10.1039/C5NR01536G · 7.39 Impact Factor
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##### Article: Quality Heterostructures from Two-Dimensional Crystals Unstable in Air by Their Assembly in Inert Atmosphere
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ABSTRACT: Many layered materials can be cleaved down to individual atomic planes, similar to graphene, but only a small minority of them are stable under ambient conditions. The rest reacts and decomposes in air, which has severely hindered their investigation and possible uses. Here we introduce a remedial approach based on cleavage, transfer, alignment and encapsulation of air-sensitive crystals, all inside a controlled inert atmosphere. To illustrate the technology, we choose two archetypal two-dimensional crystals unstable in air: black phosphorus and niobium diselenide. Our field-effect devices made from their monolayers are conductive and fully stable under ambient conditions, in contrast to the counterparts processed in air. NbSe2 remains superconducting down to the monolayer thickness. Starting with a trilayer, phosphorene devices reach sufficiently high mobilities to exhibit Landau quantization. The approach offers a venue to significantly expand the range of experimentally accessible two-dimensional crystals and their heterostructures.
Nano Letters 02/2015; DOI:10.1021/acs.nanolett.5b00648 · 13.59 Impact Factor
• ##### Article: Excitonic complexes in natural InAs/GaAs quantum dots
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ABSTRACT: The quantum confinement in a typical quantum dot (QD) is determined primarily by the nanosystem’s dimensions and average composition.We demonstrate, however, that excitonic properties of natural QDs formed in the InAs/GaAs wetting layer are governed predominantly by effects of random fluctuations of the lattice composition. It is shown that the biexciton binding energy is a very sensitive function of the lattice randomness with a nearly flat dependence on the exciton energy. The large variation in different random realizations of a QD structure is shown to lead in some cases to the reversal of the order of excitonic lines. Results of theoretical calculations correspond to statistical properties of neutral excitons and biexcitons as well as trions confined to single natural QDs studied in our microspectroscopic measurements. We observe substantial variation of the biexciton and trion binding energies as well as a correlation of the trion and the biexciton energies. The transition from the negative to the positive binding energy of the trion is also observed, which strongly supports the attribution of the observed trion to the positively charged exciton.
Physical Review B 02/2015; 91(8):085303. DOI:10.1103/PhysRevB.91.085303 · 3.74 Impact Factor
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##### Article: Insulating state in tetralayers reveals an even-odd interaction effect in multilayer graphene
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ABSTRACT: The absence of an energy gap separating valence and conduction bands makes the low-energy electronic properties of graphene and its multi-layers sensitive to electron-electron interactions. In bilayers, for instance, interactions are predicted to open a gap at charge neutrality, turning the system into an insulator, as observed experimentally. In mono and (Bernal-stacked) trilayers, interactions, although still important, do not have an equally drastic effect, and these systems remain conducting at low temperature. It may be expected that interaction effects become weaker for thicker multilayers, whose behavior should eventually converge to that of graphite. Here we show that this expectation does not correspond to reality by investigating the case of Bernal-stacked tetralayer graphene (4LG). We reveal the occurrence of a robust insulating state in a narrow range of carrier densities around charge neutrality, incompatible with the behavior expected from the single-particle band structure. The phenomenology resembles that observed in bilayers, but the stronger conductance suppression makes the insulating state in 4LG visible at higher temperature. To account for our findings, we suggest a natural generalization of the interaction-driven, symmetry-broken states proposed for bilayers. This generalization also explains the systematic even-odd effect of interactions in Bernal-stacked layers of different thickness that is emerging from experiments, and has implications for the multilayer-to-graphite crossover.
Nature Communications 01/2015; 6. DOI:10.1038/ncomms7419 · 10.74 Impact Factor
• ##### Article: Resonant Raman Scattering in MoS2
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ABSTRACT: Resonant Raman scattering in molybdenum disulfide (MoS2) is studied as a function of the sample thickness. Optical emission from 1ML, 2ML, 3ML and bulk MoS2 is investigated both at room and at liquid helium temperature. The experimental results are analysed in terms of the recently proposed attribution of the Raman peaks to multiphonon replica involving transverse acoustic phonons from the vicinity of the high-symmetry M point of the MoS2 Brillouin zone. It is shown that the corresponding processes are quenched in a few monolayer samples much stronger than the modes involving longitudinal acoustic phonons. It is also shown that along with the disappearance of multiphonon replica, the Raman modes, which are in-active in bulk become active in a few-monolayer flakes.
MRS Online Proceeding Library 01/2015; 1726. DOI:10.1557/opl.2015.168
• ##### Article: Intraband carrier dynamics in Landau-quantized multilayer epitaxial graphene
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ABSTRACT: We investigate the low-energy carrier dynamics in Landau quantized multilayer epitaxial graphene on SiC, using 14 meV photons. The THz absorption is dominated by Landau-level transitions within the conduction bands of several graphene layers with different doping. Varying the magnetic field allows us to tune the THz-induced response from induced transmission around B = 0 to induced absorption at intermediate fields (1.5 T–3.3 T) and back to induced transmission at higher fields (3.3 T–7 T). The main features of this complex response are explained by a strong dependence of the absorption on the electron temperature. Furthermore a prolonged relaxation at high fields, which is attributed to reduced scattering via optical phonons, is observed.
New Journal of Physics 12/2014; 16(12):123021. DOI:10.1088/1367-2630/16/12/123021 · 3.67 Impact Factor
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##### Article: Landau Level Spectroscopy of Electron-Electron Interactions in Graphene
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ABSTRACT: We present magneto-Raman scattering studies of electronic inter Landau level excitations in quasi-neutral graphene samples with different strengths of Coulomb interaction. The band velocity associated with these excitations is found to depend on the dielectric environment, on the index of Landau level involved, and to vary as a function of the magnetic field. This contradicts the single-particle picture of non-interacting massless Dirac electrons, but is accounted for by theory when the effect of electron-electron interaction is taken into account. Raman active, zero-momentum inter Landau level excitations in graphene are sensitive to electron-electron interactions due to the non-applicability of the Kohn theorem in this system, with a clearly non-parabolic dispersion relation.
Physical Review Letters 11/2014; 114(12). DOI:10.1103/PhysRevLett.114.126804 · 7.51 Impact Factor
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##### Article: Magnetic field tuning of exciton polaritons in a semiconductor microcavity
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ABSTRACT: We detail the influence of a magnetic field on exciton-polaritons inside a semiconductor microcavity. Magnetic field can be used as a tuning parameter for exciton and photon resonances. We discuss the change of the exciton energy, the oscillator strength and redistribution of the polariton density along the dispersion curves due to the magnetically-induced detuning. We have observed that field-induced shrinkage of the exciton wave function has a direct influence not only on the exciton oscillator strength, which is observed to increase with the magnetic field, but also on the polariton linewidth. We discuss the effect of the Zeeman splitting on polaritons which magnitude changes with the exciton Hopfield coefficient and can be modelled by independent coupling of the two spin components of excitons with cavity photons.
Physical Review B 11/2014; 91(7). DOI:10.1103/PhysRevB.91.075309 · 3.74 Impact Factor
• ##### Article: Carrier dynamics in Landau-quantized graphene featuring strong Auger scattering
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ABSTRACT: The energy spectrum of common two-dimensional electron gases consists of a harmonic (that is, equidistant) ladder of Landau levels, thus preventing the possibility of optically addressing individual transitions. In graphene, however, owing to its non-harmonic spectrum, individual levels can be addressed selectively. Here, we report a time-resolved experiment directly pumping discrete Landau levels in graphene. Energetically degenerate Landau-level transitions from n = −1 to n = 0 and from n = 0 to n = 1 are distinguished by applying circularly polarized THz light. An analysis based on a microscopic theory shows that the zeroth Landau level is actually depleted by strong Auger scattering, even though it is optically pumped at the same time. The surprisingly strong electron–electron interaction responsible for this effect is directly evidenced through a sign reversal of the pump–probe signal.
Nature Physics 11/2014; 11(1):75-81. DOI:10.1038/nphys3164 · 20.60 Impact Factor
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##### Article: Single photon emitters in exfoliated WSe2 structures
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ABSTRACT: Crystal structure imperfections in solids often act as efficient carrier trapping centers which, when suitably isolated, act as sources of single photon emission. The best known examples of such attractive imperfections are wellwidth or composition fluctuations in semiconductor heterostructures (resulting in a formation of quantum dots) and coloured centers in wide bandgap (e. g., diamond) materials. In the case of recently investigated thin films of layered compounds, the crystal imperfections may logically be expected to appear at the edges of commonly investigated few-layer flakes of these materials, exfoliated on alien substrates. Here, we report on comprehensive optical microspectroscopy studies of thin layers of tungsten diselenide, WSe2, a representative semiconducting dichalcogenide with a bandgap in the visible spectral range. At the edges of WSe2 flakes, transferred onto Si/SiO2 substrates, we discover centers which, at low temperatures, give rise to sharp emission lines (0.1 meV linewidth). These narrow emission lines reveal the effect of photon antibunching, the unambiguous attribute of single photon emitters. The optical response of these emitters is inherently linked to two-dimensional properties of the WSe2 monolayer, as they both give rise to luminescence in the same energy range, have nearly identical excitation spectra and very similar, characteristically large Zeeman effects. With advances in the structural control of edge imperfections, thin films of WSe2 may provide added functionalities, relevant for the domain of quantum optoelectronics.
Nature Nanotechnology 11/2014; 10(6). DOI:10.1038/nnano.2015.67 · 33.27 Impact Factor
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##### Article: Magnetic Field Effect on the Excitation Spectrum of a Neutral Exciton in a Single Quantum Dot
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ABSTRACT: Excitation-energy-dependent magnetospectroscopic measurements of a single GaAlAs/AlAs quantum dot were performed. A signi ficant effect of the excitation energy on the photoluminescence spectra is reported. The photo-luminescence excitation spectroscopy has been used to investigate the excitation spectrum of a single electron-hole pair - a neutral exciton in magnetic field up to 14 T. The observed resonances exhibit diamagnetic shift characteristic of an s-shell related emission. In our opinion, the creation of excited complexes involving an excited hole and a ground electron is responsible for the process.
Acta Physica Polonica Series a 11/2014; 126:1066. DOI:10.12693/APhysPolA.126.1066 · 0.60 Impact Factor
• ##### Article: High magnetic field studies of charged exciton localization in GaAs/AlxGa1-xAs quantum wells
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ABSTRACT: We report on low temperature, polarization resolved, high magnetic field (up to 23 T) photoluminescence experiments on high mobility asymmetric GaAs quantum wells. At high magnetic fields, we detect two strong emission lines of the neutral and positively charged excitons (X and X+) and a series of weaker lines of the excitons bound to ionized acceptors (AX(-)). From polarization energy splittings of these lines, we determine the hole Lande factors (g(h)) of different complexes. For X and X+, g(h) initially grows with magnetic field and then saturates at g(h) = 0.88 and 1.55, respectively; for AX(-)'s, g(h) begins from a high value (from 6 to 11 at zero field) and decreases with the field growth. This contrasting behavior is traced to the structure of valence band Landau levels, calculated numerically in the Luttinger model, beyond axial approximation. This points to the coexistence (in the same well) of mobile X and X+ with localized and interface-pressed AX(-) states. (c) 2014 AIP Publishing LLC.
Applied Physics Letters 09/2014; 105(11). DOI:10.1063/1.4896158 · 3.52 Impact Factor
• ##### Article: Hyperspectral Imaging of Exciton Photoluminescence in Individual Carbon Nanotubes Controlled by High Magnetic Fields
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ABSTRACT: Semiconducting carbon nanotubes (CNTs) provide an exceptional platform for studying one dimensional excitons (bound electron-hole pairs), but the role of defects and quenching centres in controlling emission remains controversial. Here we show that by wrapping the CNT in a polymer sheath and cooling to 4.2\,K, ultra-narrow photoluminescence (PL) emission linewidths below $80$\,$\mu$eV can be seen from individual solution processed CNTs. Hyperspectral imaging of the tubes identifies local emission sites and shows that some previously dark quenching segments can be brightened by the application of high magnetic fields and their effect on exciton transport and dynamics can be studied. Using focused high intensity laser irradiation we introduce a single defect into an individual nanotube which reduces its quantum efficiency by the creation of a shallow bound exciton state with enhanced electron-hole exchange interaction. The emission intensity of the nanotube is then reactivated by the application of the high magnetic field.
Nano Letters 08/2014; 14(9). DOI:10.1021/nl502016q · 13.59 Impact Factor

#### Publication Stats

 5k Citations 1,043.39 Total Impact Points

#### Institutions

• ###### French National Centre for Scientific Research
• Laboratoire National des Champs Magnétiques Intenses
Lutetia Parisorum, Île-de-France, France
• ###### INSA
Альтамира, Tamaulipas, Mexico
• ###### University of Warsaw
• Institute of Experimental Physics
Warszawa, Masovian Voivodeship, Poland
• ###### Technische Universität Berlin
Berlín, Berlin, Germany
• ###### Scuola Normale Superiore di Pisa
Pisa, Tuscany, Italy
• ###### National High Magnetic Field Laboratory
Tallahassee, Florida, United States
• ###### Georgia Institute of Technology
• School of Physics
Atlanta, Georgia, United States
• ###### Wroclaw University of Technology
• Institute of Physics
Vrotslav, Lower Silesian Voivodeship, Poland
• Department of Fundamental Physics
Helmantica, Castille and León, Spain
• ###### Ecole Normale Supérieure de Paris
• Laboratoire Pierre Aigrain
Paris, Ile-de-France, France
• ###### National Research Council Canada
• Institute for Microstructural Sciences (IMS)
• ###### Technische Universität Dortmund
Dortmund, North Rhine-Westphalia, Germany
• ###### McGill University
• Department of Physics
• ###### Technische Universität München
• Walter Schottky Institut (WSI)
München, Bavaria, Germany
• ###### University of California, Santa Barbara
Santa Barbara, California, United States
• ###### Polish Academy of Sciences
• Instytut Fizyki
Warsaw, Masovian Voivodeship, Poland
• ###### Institut Néel
Grenoble, Rhône-Alpes, France
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