On the signatures of non-topological patches on the surface of topological insulators

TL;DR

This paper models how topologically trivial regions on the surface of topological insulators affect local density of states, revealing signatures that can be detected via scanning tunneling spectroscopy and impact Majorana mode observations.

Contribution

It introduces a layered model for topological insulators with trivial domains, predicting local LDOS signatures of surface states that can be experimentally distinguished.

Findings

Trivial domains show suppressed LDOS in surface states.

Domain walls exhibit enhanced LDOS.

Energy dependence in STS can differentiate trivial regions.

Abstract

The non-trivial topology in the layered $\text{FeTe}_{0.55}\text{Se}_{0.45}$ (FTS) superconductor has been suggested by both theory and experiment to be strongly dependent on the Te concentration. Motivated by this together with the Te fluctuations expected from alloy disorder, we develop a simple layered model for a strong topological insulator that allows us to describe a scenario where topologically trivial domains permeate the sample. We refer to such a phase as topological domain disordered and study the local density (LDOS) of the topological surface states that can be measured using scanning tunneling spectroscopy (STS) in this phase. We find that topologically trivial domains on the surface, where one would expect the topological surface state to be absent, appear as regions of suppressed LDOS surrounded by domain walls with enhanced LDOS. Furthermore, we show that studying the energy dependence of the STS should allow us to distinguish the topologically trivial parts of the surface from other forms of disorder. Finally, we discuss implications of such local disappearance of the topological surface states for the observation of Majorana modes in vortices.