On the quantum spin Hall gap of monolayer 1T'-WTe2

TL;DR

This paper provides evidence that monolayer 1T'-WTe2 is a genuine two-dimensional quantum spin Hall insulator with a positive band gap, confirmed through theoretical calculations and experimental measurements, highlighting its potential for spintronics and quantum computing.

Contribution

The study demonstrates that monolayer 1T'-WTe2 exhibits a positive quantum spin Hall gap, establishing it as a true 2D QSH insulator through combined theoretical and experimental analysis.

Findings

Hybrid functional calculations show a positive QSH gap.

Optical measurements indicate increased interband relaxation time with fewer layers.

Transport measurements reveal Schottky barriers in ultrathin samples.

Abstract

Quantum spin Hall (QSH) materials are two-dimensional systems exhibiting insulating bulk and helical edge states simultaneously. A QSH insulator processes topologically non-trivial edge states protected by time-reversal symmetry, so that electrons can propagate unscattered. Realization of such topological phases enables promising applications in spintronics, dissipationless transport and quantum computations. Presently, realization of such QSH-based devices are limited to complicated heterostructures. Monolayer 1T'-WTe2 was predicted to be semimetallic QSH materials, though with a negative band gap. The quasi-particle spectrum obtained using hybrid functional approach shows directly that the quantum spin Hall gap is positive for monolayer 1T'-WTe2. Optical measurement shows a systematic increase in the interband relaxation time with decreasing number of layers, whereas transport measurement reveals Schottcky barrier in ultrathin samples, which is absent for thicker samples. These three independent pieces of evidence indicate that monolayer 1T'-WTe2 is likely a truly 2-dimensional quantum spin Hall insulator.