Z-dependent spin-momentum locking in monolayer 1T’-WTe₂

Monolayer 1T’-WTe₂ is a quantum spin Hall insulator with a well-defined bulk gap and helical edge states. It has been predicted to undergo a topological phase transition upon breaking the inversion symmetry with gating [1]. Recent scanning tunneling microscopy (STM) experiments by Maximenko et. al. have found a surprising linear dependence of the gap on gating voltage. We present computational results of the electronic structure of monolayer 1T’-WTe₂ with the effect of gating, using a tight-binding model derived from the Wannierised Kohn-Sham orbitals computed from density functional theory. We find that the top and bottom surfaces of the monolayer 1T’-WTe₂ exhibit opposite spin-momentum locking properties. This effect causes the STM measured gap to show a linear response upon gating.

References:
[1] Xiaofeng Qian, Junwei Liu, Liang Fu, Ju Li, Quantum spin Hall effect in two-dimensional transition metal dichalcogenides. Science 346.6215 (2014).