2D Metal-Insulator transition as a percolation transition

TL;DR

This study demonstrates that the 2D metal-insulator transition in high mobility n-GaAs heterostructures is driven by percolation due to density inhomogeneities, with experimental data supporting a classical percolation transition rather than a quantum critical point.

Contribution

The paper provides experimental evidence that the 2D MIT is a percolation transition caused by screening breakdown, challenging the quantum critical point hypothesis.

Findings

Conductivity exponent ~1.4 approaches 4/3 at low temperatures

Data inconsistent with a zero-temperature quantum critical point

Transition driven by density inhomogeneity and percolation physics

Abstract

By carefully analyzing the low temperature density dependence of 2D conductivity in undoped high mobility n-GaAs heterostructures, we conclude that the 2D metal-insulator transition in this system is a density inhomogeneity driven percolation transition due to the breakdown of screening in the random charged impurity disorder background. In particular, our measured conductivity exponent of $\sim 1.4$ approaches the 2D percolation exponent value of 4/3 at low temperatures and our experimental data are inconsistent with there being a zero-temperature quantum critical point in our system.