Topological phase transition and quantum spin Hall state in TlBiS$_2$

TL;DR

This study uses ab-initio calculations to explore how strain and electric fields can induce topological phase transitions in TlBiS$_2$, transforming it from a normal insulator into a quantum spin Hall state with surface Dirac cones.

Contribution

The paper demonstrates that strain and electric fields can induce topological phase transitions in TlBiS$_2$, supported by an effective model Hamiltonian and first-principles calculations.

Findings

Strain induces a topological phase with Dirac surface states.

Electric field can tune thin films into a quantum spin Hall state.

A critical point features a nearly linear 3D Dirac cone at the transition.

Abstract

We have investigated the bulk and surface electronic structures and band topology of TlBiS$_2$ as a function of strain and electric field using \textit{ab-initio} calculations. In its pristine form, TlBiS$_2$ is a normal insulator, which does not support any non-trivial surface states. We show however that a compressive strain along the (111) direction induces a single band inversion with Z$_2$ = (1;000), resulting in a Dirac cone surface state with a large in-plane spin polarization. Our analysis shows that a critical point lies between the normal and topological phases where the dispersion of the 3D bulk Dirac cone at the $\Gamma$-point becomes nearly linear. The band gap in thin films of TlBiS$_2$ can be tuned through an out-of-the-plane electric field to realize a topological phase transition from a trivial insulator to a quantum spin Hall state. An effective $\mathbf{k \cdot p}$ model Hamiltonian is presented to simulate our first-principles results on TlBiS$_2$.