Dimensionality-dependent type-II Weyl semimetal state in Mo${}_{0.25}$W${}_{0.75}$Te${}_2$

Abstract

Weyl nodes and Fermi arcs in type-II Weyl semimetals (WSMs) have led to lots of exotic transport phenomena. Recently, Mo${}_{0.25}$W${}_{0.75}$Te${}_2$ has been established as a type-II WSM with Weyl points located near Fermi level, which offers an opportunity to study its intriguing band structure by electrical transport measurements. Here, by selecting a special sample with the thickness gradient across two- (2D) and three-dimensional (3D) regime, we show strong evidences that Mo${}_{0.25}$W${}_{0.75}$Te${}_2$ is a type-II Weyl semimetal by observing the following two dimensionality-dependent transport features: 1) A chiral-anomaly-induced anisotropic magneto-conductivity enhancement, proportional to the square of in-plane magnetic field (B${}_{in}$${}^2$); 2) An additional quantum oscillation with thickness-dependent phase shift. Our theoretical calculations show that the observed quantum oscillation originates from a Weyl-orbit-like scenario due to the unique band structure of Mo${}_{0.25}$W${}_{0.75}$Te${}_2$. The in situ dimensionality-tuned transport experiment offers a new strategy to search for type-II WSMs.

30 pages, 5 figures