Tungsten ditelluride (WTe2) is attracting significant interest as a topological material with many interesting physical properties. Bulk WTe2 is predicted to be a type-II Weyl semimetal, whereas  in the monolayer limit, there is strong evidence that WTe2 is a 2D topological insulator that can even support superconductivity. An interesting question is how WTe2 evolves from bulk to 2D properties.

We have studied the electronic structure of WTe2 thin films with diff erent thicknesses. High quality thin fi lm samples are obtained with carrier mobility up to 5000 cm2/Vs, which enable us to resolve four main Fermi pockets from Shubnikov-de Haas (SdH) oscillations. Angle-resolved SdH oscillations reveal a crossover from three-dimensional (3D) to two-dimensional (2D) electronic systems as the WTe2 thin film samples are made thinner. Using the fi eld eff ect, the nature of the Fermi pockets in thin lm WTe2 is identi ed and the evolution of SdH oscillation frequencies is traced over di fferent sample thicknesses. It is found that both the electron and hole Fermi pockets become smaller as the samples are made thinner, which indicates the overlap between conduction and valence bands is getting smaller. Our work shed lights on the thickness-dependent evolution of electronic structure when WTe2 samples transition from 3D Weyl semimetals into 2D topological insulators.

F. Xiang et al, https://arxiv.org/abs/1703.02741