Termination of two-dimensional metallic conduction near metal-insulator transition in a Si/SiGe quantum well

TL;DR

This study investigates the low-temperature transport properties of a Si/SiGe quantum well near the metal-insulator transition, revealing non-monotonic conductivity behavior and suggesting the metallic phase may be a finite temperature phenomenon.

Contribution

It provides new insights into the temperature-dependent conductivity near the 2D metal-insulator transition in Si/SiGe quantum wells, highlighting the potential finite temperature nature of the metallic phase.

Findings

Observation of non-monotonic temperature dependence of conductivity.

Downturn temperature follows a power law with mobility.

Metallic behavior may only exist at finite temperatures.

Abstract

We report in this Letter our recent low temperature transport results in a Si/SiGe quantum well with moderate peak mobility. An apparent metal-insulating transition is observed. Within a small range of densities near the transition, the conductivity $\sigma$ displays non-monotonic temperature dependence. After an initial decrease at high temperatures, $\sigma$ first increases with decreasing temperature T, showing a metallic behavior. As T continues decreasing, a downturn in $\sigma$ is observed. This downturn shifts to a lower T at higher densities. More interestingly, the downturn temperature shows a power law dependence on the mobility at the downturn position, suggesting that a similar downturn is also expected to occur deep in the apparent metallic regime at albeit experimentally inaccessible temperatures. This thus hints that the observed metallic phase in 2D systems might be a finite temperature effect.