Possible Metal/Insulator Transition at B=0 in Two Dimensions

TL;DR

This study investigates the resistivity behavior of a high-mobility two-dimensional electron system in silicon at zero magnetic field, revealing a possible metal-insulator transition near a critical electron density.

Contribution

It provides experimental evidence for a metal-insulator transition at B=0 in two dimensions, challenging traditional localization theories.

Findings

Resistivity drops sharply below 1-2 K at certain densities

No localization evidence down to 20 mK for densities above critical

Resistivity scales with temperature, indicating a phase transition

Abstract

We have studied the zero magnetic field resistivity of unique high- mobility two-dimensional electron system in silicon. At very low electron density (but higher than some sample-dependent critical value, $n_{cr}\sim 10^{11}$ cm$^{-2}$), CONVENTIONAL WEAK LOCALIZATION IS OVERPOWERED BY A SHARP DROP OF RESISTIVITY BY AN ORDER OF MAGNITUDE with decreasing temperature below 1--2 K. No further evidence for electron localization is seen down to at least 20 mK. For $n_s<N_{cr}$, the sample is insulating. The resistivity is empirically found to SCALE WITH TEMPERATURE BOTH BELOW AND ABOVE $n_{cr}$ WITH A SINGLE PARAMETER which approaches zero at $n_s=n_{cr}$ suggesting a metal/ insulator phase transition.