Kinetic properties of two-dimensional metal systems

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Abstract
The two-dimensional degenerate Fermi gas of electrons interacting with phonons is considered. The basic mechanisms of momentum relaxation in such a system, associated with electron-phonon, phonon-phonon and electron-electron collisions, are shown to be qualitatively different from similar mechanisms in an ordinary three-dimensional metal. The physical explanation for this is that the two-dimensional system of interacting electrons and phonons breaks down into almost isolated groups, between which momentum transfer occurs through very slow, staged superdiffusion (mixing) processes. With certain structures of the Fermi surface, quasimomentum transfer through electron-electron collisions is insignificant; hence such collisions are not an efficient relaxation mechanism. In this paper an efficient method is suggested for deriving superdiffusion equations, based on the detailed-balance conditions in the electron-phonon system. A theory of low-temperature transport phenomena is developed for pure two-dimensional metals. As has been found, the electrical and thermal conductivity coefficients under certain conditions may be anomalously high, showing a qualitatively different behaviour from that observed in three-dimensional metals. The electrical conductivity is analysed for a metal whose electron spectrum is nearly two-dimensional, as well as for a metal in which the prevailing mechanism of electron scattering is due to impurities. The effect of specifically two-dimensional relaxation mechanisms upon sound absorption is analysed. The possibility of observing such effects experimentally in layered metal compounds of intercalated graphite type is discussed.