Surface Acoustic Wave Propagation and Inhomogeneities in Low Density Two-Dimensional Electron Systems Near the Metal-Insulator Transition

TL;DR

This study investigates surface acoustic wave behavior in low-density 2D electron systems near the metal-insulator transition, revealing inhomogeneities that challenge existing models and impact understanding of the transition.

Contribution

It provides new insights into SAW interactions with low-density 2DES and highlights the significance of inhomogeneities near the metal-insulator transition.

Findings

Surface acoustic wave velocity shift measurements in low-density 2DES.

Inadequacy of simple conductivity models to explain observations.

Inhomogeneities play a crucial role at low electron densities.

Abstract

We have measured the surface acoustic wave velocity shift in a GaAs/AlGaAs heterostructure containing a two-dimensional electron system (2DES) in a low-density regime ($<$ $10^{10}$ cm$^{-2}$) at zero magnetic field. The interaction of the surface acoustic wave with the 2DES is not well described by a simple model using low-frequency conductivity measurements. We speculate that this conflict is a result of inhomogeneities in the 2DES which become very important at low density. This has implications for the putative metal-insulator transition in two dimensions.