Topological nature of step edge states on the surface of topological crystalline insulator Pb$_{0.7}$Sn$_{0.3}$Se

TL;DR

This paper demonstrates both theoretically and experimentally that step edges on the surface of the topological crystalline insulator Pb$_{0.7}$Sn$_{0.3}$Se host topologically protected 1D states, stabilized by emergent symmetries and affected by magnetic fields.

Contribution

It establishes the topological origin of step edge states on a TCI surface, highlighting the role of emergent particle-hole symmetry and experimental signatures of symmetry breaking.

Findings

Topological stability of step edge states due to particle-hole symmetry

Experimental evidence of particle-hole symmetry breaking signatures

Effects of magnetic field on 1D bound states

Abstract

In addition to novel surface states, topological insulators can also exhibit robust gapless states at crystalline defects. Step edges constitute a class of common defects on the surface of crystals. In this work we establish the topological nature of one-dimensional (1D) bound states localized at step edges of the [001] surface of a topological crystalline insulator (TCI) Pb$_{0.7}$Sn$_{0.3}$Se, both theoretically and experimentally. We show that the topological stability of the step edge states arises from an emergent particle-hole symmetry of the surface low-energy physics, and demonstrate the experimental signatures of the particle-hole symmetry breaking. We also reveal the effects of an external magnetic field on the 1D bound states. Our work suggests the possibility of similar topological step edge modes in other topological materials with a rocks-salt structure.