Field Laboratory in France, the Tsukuba Magnet Laboratory in Japan or the National High Magnetic Field Laboratory in the United States. The most direct experimental technique to resolve the electronic structure of crystals in the momentum-energy space (see reciprocal lattice), and, consequently, the Fermi surface, is the angle-resolved photoemission spectroscopy (ARPES). An example of the Fermi surface of superconducting cuprates measured by ARPES is shown in the figure 3. With positron annihilation it is also possible to determine the Fermi surface as the annihilation process conserves the momentum of the initial particle. Since a positron in a solid will thermalize prior to annihilation, the annihilation radiation carries the information about the electron momentum. The corresponding experimental technique is called angular correlation of electron positron annihilation radiation (ACAR) as it measures the angular deviation from of both annihilation quanta. In this way it is possible to probe the electron momentum density of a solid and determine the Fermi surface. Furthermore, using spin polarized positrons, the momentum distribution for the two spin states in magnetized materials can be obtained. ACAR has many advantages and disadvantages compared to other experimental techniques: It does not rely on UHV conditions, cryogenic temperatures, high magnetic fields or fully ordered alloys. However, ACAR needs samples with a low vacancy concentration as they act as effective traps for positrons. In this way, the first determination of a smeared Fermi surface in a 30% alloy was obtained in 1978. See also Fermi energy Brillouin zone Fermi surface of superconducting cuprates Kelvin probe force microscope Luttinger's theorem References External links Experimental Fermi surfaces of some superconducting cuprates and strontium ruthenates in "Angle-resolved photoemission spectroscopy of the cuprate superconductors (Review Article)" (2002) Experimental Fermi surfaces of some cuprates, transition metal dichalcogenides, ruthenates, and iron-based superconductors in "ARPES experiment in fermiology of quasi-2D metals (Review Article)" (2014) Condensed matter physics Electric and magnetic fields in matter Fermi–Dirac statistics