Surface-state spin textures in strained bulk HgTe: strain-induced topological phase transitions

TL;DR

This paper investigates how uniaxial strain induces topological phase transitions in bulk HgTe, affecting the spin textures of surface states and revealing a flip in the winding number without changing bulk invariants.

Contribution

It introduces a detailed analysis of strain-induced topological phase transitions in HgTe and links spin textures to mirror Chern numbers and orbital composition.

Findings

Strain opens a band gap making HgTe a strong 3D topological insulator.

Surface spin textures undergo a topological phase transition with increasing strain.

Winding number of surface state spin texture flips without bulk invariant change.

Abstract

The opening of a band gap due to compressive uniaxial strain renders bulk HgTe a strong three-dimensional topological insulators with protected gapless surface states at any surface. By employing a six-band k.p model, we determine the spin textures of the topological surface states of strained HgTe using their close relations with the mirror Chern numbers of the system and the orbital composition of the surface states. We show that at surfaces with C2v point group symmetry an increase in the strain magnitude triggers a topological phase transition where the winding number of the surface state spin texture is flipped while the four topological invariants characterizing the bulk band structure of the material are unchanged.