Thermal robustness of the quantum spin Hall phase in monolayer WTe$_2$

TL;DR

This study uses first-principle simulations to analyze how thermal effects influence the electronic and topological properties of monolayer WTe₂, revealing robustness of the quantum spin Hall phase up to and beyond room temperature.

Contribution

It provides a comprehensive first-principle analysis of temperature effects on monolayer WTe₂, highlighting the robustness of its topological phase against thermal perturbations.

Findings

Thermal expansion slightly increases the band gap.

Electron-phonon coupling causes a small reduction in band inversion.

Topological phase remains stable up to and above room temperature.

Abstract

Monolayer 1T'-WTe$_2$ has been the first two-dimensional crystal where a quantum spin Hall phase was experimentally observed. In addition, recent experiments and theoretical modeling reported the presence of a robust excitonic insulating phase. While first-principles calculations with hybrid functionals and several measurements at low temperatures suggest the presence of a band gap of the order of 50 meV, experiments could confirm the presence of the helical edge states only up to 100 K. Here, we study with first-principle simulations the temperature effects on the electronic structure of monolayer 1T'-WTe$_2$ and consider the contributions of both thermal expansion and electron-phonon coupling. First, we show that thermal expansion is weak but tends to increase the indirect band gap. Then, we calculate the effect of electron-phonon coupling on the band structure with non-perturbative methods and observe a small reduction of the band inversion with increasing temperature. Notably, the topological phase and the presence of a finite gap are found to be particularly robust to thermal effects up to and above room temperature.