Testing Topological Protection of Edge States in Hexagonal Quantum Spin Hall Candidate Materials

TL;DR

This paper investigates the topological protection mechanisms of edge states in hexagonal quantum spin Hall materials, highlighting the effects of crystal symmetry and magnetic fields on their robustness and potential for room-temperature applications.

Contribution

It reveals how crystal symmetry influences topological protection in QSH edge states and predicts experimental signatures for their crystalline and helicity properties.

Findings

Armchair QSH edge states remain gapless under in-plane magnetic fields.

Out-of-plane magnetic fields open a measurable gap in edge states.

Experimental signatures for crystalline protection and helicity are proposed.

Abstract

We analyze the detailed structure of topological edge mode protection occuring in hexagonal quantum spin Hall (QSH) materials. We focus on bismuthene, antimonene, and arsenene on a SiC substrate, which, due to their large bulk gap, may offer new opportunities for room-temperature QSH applications. While time reversal symmetry is responsible for the principal symmetry protected character of QSH states, the hexagonal edge terminations yield further aspects of crystal symmetry which affect the topological protection. We show that armchair QSH edge states remain gapless under an in-plane magnetic field in the direction along the edge, a hallmark of their topological crystalline protection. In contrast, an out-of-plane magnetic field opens a gap of the order of a few meV within realistic ranges of parameters. We use these intriguing signatures of armchair QSH edge states to predict experimentally testable fingerprints of their additional topological crystalline character and their helicity emerging in tunneling spectroscopy and ballistic magnetotransport.