Unexpected Behavior of the Local Compressibility Near the B=0 Metal-Insulator Transition

TL;DR

This study investigates the local electronic compressibility of a two-dimensional hole gas near the B=0 metal-insulator transition, revealing unexpected inhomogeneity and deviations from mean-field predictions in the insulating phase.

Contribution

It provides the first detailed measurement of local compressibility behavior across the transition, highlighting a thermodynamic change and spatial inhomogeneity in the insulating phase.

Findings

Compressibility matches Hartree-Fock theory in metallic phase

Deviates significantly and becomes inhomogeneous in insulating phase

Transition point aligns with critical transport density

Abstract

We have measured the local electronic compressibility of a two-dimensional hole gas as it crosses the B=0 Metal-Insulator Transition. In the metallic phase, the compressibility follows the mean-field Hartree-Fock (HF) theory and is found to be spatially homogeneous. In the insulating phase it deviates by more than an order of magnitude from the HF predictions and is spatially inhomogeneous. The crossover density between the two types of behavior, agrees quantitatively with the transport critical density, suggesting that the system undergoes a thermodynamic change at the transition.