Mesoscopic Behavior Near a Two-Dimensional Metal-Insulator Transition

TL;DR

This paper investigates conductance fluctuations in a two-dimensional electron gas near the metal-insulator transition, revealing critical behavior and multiple decay exponents linked to Coulomb correlations and screening effects.

Contribution

It provides the first detailed analysis of conductance fluctuation spectra and their exponents across the transition, highlighting critical dielectric response behavior.

Findings

Identification of multiple decay exponents in conductance fluctuation spectra.

Observation of non-monotonic dependence of fluctuation exponents on conductivity.

Evidence of critical Coulomb correlations near the transition point.

Abstract

We study conductance fluctuations in a two-dimensional electron gas 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 $\sigma\sim 0.1 e^{2}/h$, we find a third exponent (1/v_i) in the shortest samples, and non-monotonic dependence of v_i and v_l on \sigma. We study the dependence of v_i, v_l, v_h, and the variances of corresponding fluctuations on \sigma, sample size, and temperature. The anomalies near $\sigma\simeq 0.1 e^{2}/h$ indicate that the dielectric response and screening length are critically behaved, i.e. that Coulomb correlations dominate the physics.