Microfocus laser-ARPES on encapsulated mono-, bi-and few-layer 1 T ’-WTe 2

few-layer 1T’-WTe2 Irène Cucchi, Ignacio Gutiérrez-Lezama, 2 Edoardo Cappelli, Siobhan McKeown Walker, Flavio Y. Bruno, Giulia Tenasini, 2 Lin Wang, 2, ∗ Nicolas Ubrig, 2 Céline Barreteau, † Enrico Giannini, Marco Gibertini, 3 Anna Tamai, Alberto F. Morpurgo, 2 and Felix Baumberger 4 Department of Quantum Matter Physics, University of Geneva, 24 quai Ernest Ansermet, CH-1211 Geneva, Switzerland Group of Applied Physics, University of Geneva, 24 Quai Ernest Ansermet, CH-1211 Geneva, Switzerland National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland Abstract 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 monobiand 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.