Electronic properties of monolayer 1T'-WTe₂

Abstract

Quantum spin Hall (QSH) insulators are promising candidate for electronic applications, for their time-reversal protected backscattering-free edge states, with a pair of counterpropagating, helical electronic modes. Transport experiment has shown monolayer 1T'-WTe₂ displaying QSH edge modes persisting up to 100 K. Here we present a 4-orbital tight-binding (TB) model for describing the low-energy physics of monolayer WTe₂ in 1T’ structure. Based on the symmetries analysis and first-principles calculations, 𝑑_x²-𝑦²-type orbitals from 2 M atoms and 𝑝_x-type orbitals from 2 out of the 4 X atoms are chosen as the basis. Hopping parameters of the TB model are fitted according to band structure calculated in the density functional theory (DFT) framework. The TB model includes all the hopping within nearest neighbor unit cells. It is able to well reproduce the energy bands −0.3eV to +0.75 eV around Fermi energy. Edge states for 4 different cuts of nanoribbon along the glide mirror preserving direction are calculated with Green’s function method, which confirms the nontrivial Z₂ topological phases. The model is easily tunable to capture both semi-metallic and full gapped scenarios, based on the idea of applying strain on one direction. The TB models developed here is sufficient to describe the low-energy physics in monolayers 1T'-WTe₂, and they can serve as basis for further study for their simplicity and high accuracy. The TB model here can be also easily applied for other monolayer 1T’ transitional metal dichalcogenides MX₂ (M=W, Mo; X=S, Se, Te).

Date of Award	2019
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology