Quantum phase transition in ultrahigh mobility SiGe/Si/SiGe two-dimensional electron system

TL;DR

This study investigates the metal-insulator transition in ultra-high mobility SiGe/Si/SiGe quantum wells, revealing a quantum phase transition characterized by a critical electron density lower than the divergence point of effective mass, with significant resistance changes at low temperatures.

Contribution

It demonstrates the occurrence of a quantum phase transition in ultra-high mobility SiGe/Si/SiGe systems, contrasting with lower-mobility samples, and links the transition to changes in resistance behavior near the divergence of effective mass.

Findings

Critical electron density for MIT is lower than the divergence point of effective mass.

Resistance drops by more than an order of magnitude below 1 K.

Metallic temperature dependence of resistance is enhanced near the transition.

Abstract

The metal-insulator transition (MIT) is an exceptional test bed for studying strong electron correlations in two dimensions in the presence of disorder. In the present study, it is found that in contrast to previous experiments on lower-mobility samples, in ultra-high mobility SiGe/Si/SiGe quantum wells the critical electron density, $n_{\text{c}}$, of the MIT becomes smaller than the density, $n_{\text{m}}$, where the effective mass at the Fermi level tends to diverge. Near the topological phase transition expected at $n_{\text{m}}$, the metallic temperature dependence of the resistance should be strengthened, which is consistent with the experimental observation of more than an order of magnitude resistance drop with decreasing temperature below $\sim1$ K.