Disorder-driven topological phase transition in Bi2Se3 films

TL;DR

This paper demonstrates that increasing disorder in Bi2Se3 topological insulator films can induce a phase transition from a topologically non-trivial metallic state to a trivial insulating state, challenging the notion of perfect topological protection.

Contribution

It provides experimental evidence that disorder can cause a topological phase transition without breaking time reversal symmetry in Bi2Se3 films.

Findings

Disorder causes loss of topological surface states in Bi2Se3.

A critical disorder level leads to a transition to an insulating phase.

Topological phase transition occurs without symmetry breaking.

Abstract

Topological insulators (TI) are a phase of matter that host unusual metallic states on their surfaces. Unlike the states that exist on the surface of conventional materials, these so-called topological surfaces states (TSS) are protected against disorder-related localization effects by time reversal symmetry through strong spin-orbit coupling. By combining transport measurements, angle-resolved photo-emission spectroscopy and scanning tunneling microscopy, we show that there exists a critical level of disorder beyond which the TI Bi2Se3 loses its ability to protect the metallic TSS and transitions to a fully insulating state. The absence of the metallic surface channels dictates that there is a change in topological character, implying that disorder can lead to a topological phase transition even without breaking the time reversal symmetry. This observation challenges the conventional notion of topologically-protected surface states, and will provoke new studies as to the fundamental nature of topological phase of matter in the presence of disorder.