Robust topological insulator surface conduction under strong surface disorder

TL;DR

This paper demonstrates that the edge conduction in 2D topological insulators remains robust against strong non-magnetic boundary disorder, with disorder affecting properties like Fermi velocity and density of states but not destroying conduction.

Contribution

It reveals that topological insulator edge states are resilient to boundary disorder and details how disorder influences their electronic properties without compromising conduction.

Findings

Edge states remain conducting despite boundary disorder.

Disorder reduces Fermi velocity and increases density of states.

States shift to the boundary at very large disorder levels.

Abstract

Topological insulators are characterized by specially protected conduction on their outer boundaries. We show that the protected edge conduction exhibited by 2-D topological insulators (and also Chern insulators) is independent of non-magnetic boundary disorder. In particular, the edge states residing inside the bulk gap remain conducting even when edge state inhomogeneities destroy the characteristic linear Dirac relation between energy and momentum. The main effects of boundary disorder on the in-gap states are to decrease the Fermi velocity, increase the density of states, pull the states into the disordered region if spin is conserved, and at very large disorder shift the states to the boundary between the disordered edge and the clean bulk. These effects, which may be useful for device engineering, are controlled by a resonance between the disordered edge and the bulk bands. The resonance's energy is set by the bulk band width; protection of the in-gap edge states' plane-wave character is controlled by the bulk band width, not the bulk band gap.