Temperature-induced topological phase transitions: promoted vs. suppressed non-trivial topology

TL;DR

This study uses first-principles calculations to explore how temperature and phonon interactions influence topological phase transitions in BiTl(S,Se)$_2$, revealing temperature-dependent promotion or suppression of non-trivial topology.

Contribution

It uncovers the role of phonon symmetry in temperature-induced topological phase transitions in BiTl(S,Se)$_2$, highlighting how different phonon modes promote or suppress topological phases.

Findings

In BiTlS$_2$, high temperature promotes topological phase.

In BiTlSe$_2$, low temperature is required for topological phase.

Phonon symmetry determines the promotion or suppression of topology.

Abstract

We determine the topological phase diagram of BiTl(S$_{1-\delta}$Se$_{\delta}$)$_2$ as a function of doping and temperature from first-principles calculations. Due to electron\textendash phonon interaction, the bands are renormalized at finite temperature, allowing for a transition between the trivial ($Z_2=0$) and non-trivial ($Z_2=1$) topological phase. We find two distinct regions of the phase diagram with non-trivial topology. In BiTlS$_2$, the phonons promote the crystal to the topological phase at high temperature, while in BiTlSe$_2$, the topological phase exists only at low temperature. This behaviour is explained by the symmetry of the phonon coupling potential, whereby the even phonon modes (whose potential is even under inversion) promote the topological phase and the odd phonon modes promote the trivial phase.