Evidence for Topological States and a Lifshitz Transition in Metastable 2M-WSe2

Abstract

In recent years, T_d transition metal dichalcogenides have been heavily explored for their type-II Weyl topology, gate-tunable superconductivity, and nontrivial edge states in the monolayer limit. Here, the Fermi surface characteristics and fundamental transport properties of similarly structured 2M-WSe₂ bulk single crystals are investigated. The measurements of the angular dependent Shubnikov–de Haas oscillations, with support from first-principles calculations, reveal multiple three- and two-dimensional Fermi pockets, one of which exhibits a nontrivial Berry's phase. In addition, it is shown that the electronic properties of 2M-WSe₂ are similar to those of orthorhombic MoTe₂ and WTe₂, having a single dominant carrier type at high temperatures that evolves into coexisting electron and hole pockets with near compensation at temperatures below 100 K, suggesting the existence of a Lifshitz transition. Altogether, the observations provide evidence towards the topologically nontrivial electronic properties of 2M-WSe₂ and motivate further investigation on the topological properties of 2M transition metal dichalcogenides in the atomically thin limit.