Tunable Anderson metal-insulator transition in quantum-spin Hall insulators

TL;DR

This study numerically investigates disorder effects in BHZ models of quantum spin-Hall insulators, revealing an exotic metallic phase influenced by Berry phase and model parameters, with different transition behaviors in InAs/GaSb and HgTe/CdTe systems.

Contribution

It uncovers the existence of an exotic metallic phase in certain BHZ models and clarifies the conditions for different topological phase transitions under disorder.

Findings

An exotic metallic phase can emerge between QSHI and normal insulator in InAs/GaSb BHZ model.

Direct QSHI to normal insulator transition occurs in HgTe/CdTe BHZ model.

The metallic phase is linked to Berry phase effects and can exist inside and outside the energy gap.

Abstract

We numerically study disorder effects in Bernevig-Hughes-Zhang (BHZ) model, and find that Anderson transition of quantum spin-Hall insulator (QSHI) is determined by model parameters. The BHZ Hamiltonian is equivalent to two decoupled spin blocks that belong to the unitary class. In contrast to the common belief that a two-dimensional unitary system scales to an insulator except at certain critical points, we find, through calculations scaling properties of the localization length, level statistics, and participation ratio, that a possible exotic metallic phase emerges between a QSHI and a normal insulator phases in InAs/GaSb-type BHZ model. On the other hand, direct transition from a QSHI to a normal insulator is found in HgTe/CdTe-type BHZ model. Furthermore, we show that the metallic phase originates from the Berry phase and can survive both inside and outside the gap.