Strong potential impurities on the surface of a topological insulator

TL;DR

This paper investigates how strong potential impurities affect the surface states of topological insulators, revealing significant modifications and impurity resonances that challenge the assumed robustness of these materials.

Contribution

It provides a detailed lattice model analysis showing how strong impurities alter the Dirac surface states and penetrate into the bulk, impacting topological protection.

Findings

Impurity resonances create a peak near the Dirac point.

The Dirac point is split into two off-center nodes.

Impurity states penetrate up to 10 layers into the bulk.

Abstract

Topological insulators (TIs) are said to be stable against non-magnetic impurity scattering due to suppressed backscattering in the Dirac surface states. We solve a lattice model of a three-dimensional TI in the presence of strong potential impurities and find that both the Dirac point and low-energy states are significantly modified: low-energy impurity resonances are formed that produce a peak in the density of states near the Dirac point, which is destroyed and split into two nodes that move off-center. The impurity-induced states penetrate up to 10 layers into the bulk of the TI. These findings demonstrate the importance of bulk states for the stability of TIs and how they can destroy the topological protection of the surface.