The Observation of Percolation-Induced 2D Metal-Insulator Transition in a Si MOSFET

TL;DR

This study demonstrates that the 2D metal-insulator transition in high-mobility Si MOSFETs is driven by percolation due to density inhomogeneities, with conductivity vanishing as a power law near the critical density.

Contribution

It provides evidence that the 2D metal-insulator transition is a percolation transition caused by density inhomogeneities, supported by conductivity scaling and magnetoresistance measurements.

Findings

Conductivity follows a power law near the critical density with exponent ~1.2.

Metallic behavior is well-described by semi-classical Boltzmann theory.

Weak localization effects are observed in the metallic phase.

Abstract

By analyzing the temperature ($T$) and density ($n$) dependence of the measured conductivity ($\sigma$) of 2D electrons in the low density ($\sim10^{11}$cm$^{-2}$) and temperature (0.02 - 10 K) regime of high-mobility (1.0 and 1.5 $\times 10^4$ cm$^2$/Vs) Si MOSFETs, we establish that the putative 2D metal-insulator transition is a density-inhomogeneity driven percolation transition where the density-dependent conductivity vanishes as $\sigma (n) \propto (n - n_p)^p$, with the exponent $p \sim 1.2$ being consistent with a percolation transition. The `metallic' behavior of $\sigma (T)$ for $n > n_p$ is shown to be well-described by a semi-classical Boltzmann theory, and we observe the standard weak localization-induced negative magnetoresistance behavior, as expected in a normal Fermi liquid, in the metallic phase.