Thermodynamic density of states of two-dimensional GaAs systems near the apparent metal-insulator transition

TL;DR

This study investigates the thermodynamic and transport properties of two-dimensional GaAs systems near the apparent metal-insulator transition, revealing a percolation transition at lower density without thermodynamic anomalies.

Contribution

It provides combined resistivity and compressibility measurements showing a percolation transition distinct from the crossover, explained by nonlinear screening theory.

Findings

Compressibility matches nonlinear screening theory.

Resistivity shows scaling near percolation threshold.

Percolation occurs at lower density than the crossover.

Abstract

We perform combined resistivity and compressibility studies of two-dimensional hole and electron systems which show the apparent metal-insulator transition - a crossover in the sign of dR/dT with changing density. No thermodynamic anomalies have been detected in the crossover region. Instead, despite a ten-fold difference in r_s, the compressibility of both electrons and holes is well described by the theory of nonlinear screening of the random potential. We show that the resistivity exhibits a scaling behavior near the percolation threshold found from analysis of the compressibility. Notably, the percolation transition occurs at a much lower density than the crossover.