Dielectric properties of the electron glass

Abstract

The dielectric-constant matrix of a system of electrons that have been localized by disorder is calculated as a function of frequency and distance. It is shown that the basic polarization process in these systems is quite different from those with extended electrons, as the electronic transitions can only occur by phonon-mediated hops between localized states. It is also argued that the random-phase approximation is not adequate for such systems, as the correct account for the excitation energies of the system requires inclusion of electron-hole interaction. Our analysis provides an expression for screening length that shows a basic departure from the Thomas-Fermi approximation. On the basis of our results for polarizability, we also argue that a soft Coulomb gap for electron-hole excitations should exist to provide dielectric stability to the system.