The fate of topological-insulator surface states under strong disorder

TL;DR

This paper explores how strong surface disorder affects topological insulator surface states, revealing a transition from Dirac cone destruction to reemergence of surface states due to an interface with an Anderson insulator.

Contribution

It demonstrates the complex impact of strong disorder on topological surface states, including the reappearance of Dirac-like states at high disorder levels.

Findings

Moderate disorder destroys the Dirac cone and causes diffusive metallic behavior.

Strong disorder leads to the reemergence of Dirac-like surface states.

Surface states under strong disorder can be understood as an interface between topological and Anderson insulators.

Abstract

Three-dimensional topological insulators feature Dirac-like surface states which are topologically protected against the influence of weak quenched disorder. Here we investigate the effect of surface disorder beyond the weak-disorder limit using large-scale numerical simulations. We find two qualitatively distinct regimes: Moderate disorder destroys the Dirac cone and induces diffusive metallic behavior at the surface. Even more remarkably, for strong surface disorder a Dirac cone reappears, as new weakly disordered "surface" states emerge in the sample beneath the disordered surface layer, which can be understood in terms of an interface between a topological and an Anderson insulator. Together, this demonstrates the drastic effect of disorder on topological surface states, which cannot be captured within effective two-dimensional models for the surface states alone.