Low-temperature d.c. transport in anisotropic dirty thin dielectric films

A theory of low-temperature ohmic dc transport in dirty 2D quasi-one dimensional electronic crystals, such as charge-density wave (CDWs) thin films, is presented. At low temperatures we find that Efros-Shklovskii (ES) variable-range hopping (VRH) laws dominate the transport. At the lowest energies of the problem we find a usual impurity-independent linear Coulomb-gap (CG), g( ) ∝ , in the single particle density of states. An ES law for the resistivity follows with the usual exponent 1/2: ρ ∝ exp[(TES /T )1/2], but with TES increasing with disorder. At higher energies, the peculiar screening of the interactions leads to a crossover to an unusual CG which is quadratic, g( ) ∝ , for a 2D system and impurity dependent. This leads to a temperature crossover to an unusual ES law ρ ∝ exp[(T3/5/T )3/5], with T3/5 increasing with disorder. At even higher temperatures a crossover to activation takes place. The results should apply to mono-layers of 4kF CDWs.