Fine structure of hopping conductance fluctuations in finite-size semiconductors.

Abstract

The plateau paradox---the absence of flat regions from incoherent mesoscopic oscillations---is investigated. Random reproducible oscillations of the conductance G versus the gate voltage ${\mathit{V}}_{\mathit{g}}$ have been observed in the past few years in different field-effect structures in the strongly localized regime. The presence of plateaus should be a sign of the hopping nature of transport that is believed to be responsible for the existence of mesoscopic oscillations. The part p of the mesoscopic pattern that should be occupied by plateaus in one dimension is calculated analytically with the use of a traditional approach for hopping. The value p turns out to be parametrically small and decreases slowly with the sample length. To interpret the absence of plateaus in two-dimensional systems, two phenomena neglected in the traditional approach---Hubbard correlation between occupations of different sites and Coulomb interaction of electrons---are discussed. A mechanism for the suppression of Hubbard correlations in a disordered system is proposed. The influence of Coulomb effects on mesoscopic oscillations for the experiments of interest is shown to be sufficient to change dramatically the structure of a mesoscopic pattern.