Mesoscopic behavior near a two-dimensional metal-insulator transition

Abstract

We study conductance fluctuations in a two-dimensional electron system as a function of chemical potential (or gate voltage) from the strongly insulating to the metallic regime. Power spectra of the fluctuations decay with two distinct exponents ${(1/v}_{l}$ and ${1/v}_{h}).$ For conductivity $\ensuremath{\sigma}\ensuremath{\sim}{0.1e}^{2}/h,$ we find a third exponent ${(1/v}_{i})$ in the shortest samples, and nonmonotonic dependence of ${v}_{i}$ and ${v}_{l}$ on \ensuremath{\sigma}. We study the dependence of ${v}_{i},$ ${v}_{l},$ ${v}_{h},$ and the variances of corresponding fluctuations on \ensuremath{\sigma}, sample size, and temperature. The anomalies near $\ensuremath{\sigma}\ensuremath{\simeq}{0.1e}^{2}/h$ indicate that the dielectric response and screening length are critically behaved, i.e., that Coulomb correlations dominate the physics.