Two-dimensional crystals of semimetallic van der Waals materials hold much potential for the realization of novel phases, as exemplified by the recent discoveries of a polar metal in few layer 1T'-WTe2 and of a quantum spin Hall state in monolayers of the same material. Understanding these phases is particularly challenging because little is known from experiment about the momentum space electronic structure of ultrathin 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 with monolayer graphene a flake of WTe2 comprising regions of different thickness. 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.
@article{arxiv.1811.04629,
title = {Microfocus laser-ARPES on encapsulated mono-, bi-, and few-layer 1T'-WTe$_2$},
author = {Irène Cucchi and Ignacio Gutiérrez-Lezama and Edoardo Cappelli and Siobhan McKeown Walker and Flavio Y. Bruno and Giulia Tenasini and Lin Wang and Nicolas Ubrig and Céline Barreteau and Enrico Giannini and Marco Gibertini and Anna Tamai and Alberto F. Morpurgo and Felix Baumberger},
journal= {arXiv preprint arXiv:1811.04629},
year = {2019}
}