Microfocus laser-ARPES on encapsulated mono-, bi- and few-layer 1T'-WTe₂

The recent discoveries of a quantum spin Hall state and of ferroelectric polarization in exfoliated crystals of 1T'-WTe₂ demonstrate the potential of semimetallic van der Waals materials for the realization of novel phases. However, current understanding of these phases is largely based on theoretical simulations since little is known from experiment about the electronic structure of few-layer crystals. Here, we report direct electronic structure measurements of exfoliated mono- bi- and few-layer 1T'-WTe₂ by laser-based micro-focus angle resolved photoemission. This is achieved by encapsulating a flake of WTe₂ comprising regions of different thickness with monolayer graphene. Our data support the recent identification of a quantum spin Hall state in monolayer 1T'-WTe₂ and reveal strong signatures of the broken inversion symmetry in the bilayer. We finally discuss the sensitivity of encapsulated samples to contaminants following exposure to ambient atmosphere.