Disorder-Induced Multiple Transition involving Z2 Topological Insulator

TL;DR

This paper investigates how disorder affects two-dimensional Z2 topological insulators, revealing a complex phase diagram with multiple transitions between insulating and metallic phases driven by disorder.

Contribution

It provides a detailed numerical analysis of disorder-induced phase transitions in Z2 topological insulators, including the discovery of a metallic region separating topologically distinct insulating phases.

Findings

Disorder causes multiple phase transitions, including to and from metallic states.

A metallic region exists between topologically distinct insulating phases.

The phase behavior is explained by band gap renormalization and Anderson localization.

Abstract

Effects of disorder on two-dimensional Z2 topological insulator are studied numerically by the transfer matrix method. Based on the scaling analysis, the phase diagram is derived for a model of HgTe quantum well as a function of disorder strength and magnitude of the energy gap. In the presence of sz non-conserving spin-orbit coupling, a finite metallic region is found that partitions the two topologically distinct insulating phases. As disorder increases, a narrow-gap topologically trivial insulator undergoes a series of transitions; first to metal, second to topological insulator, third to metal, and finally back to trivial insulator. We show that this multiple transition is a consequence of two disorder effects; renormalization of the band gap, and Anderson localization. The metallic region found in the scaling analysis corresponds roughly to the region of finite density of states at the Fermi level evaluated in the self-consistent Born approximation.