Discovery of Weyl semimetal state violating Lorentz invariance in MoTe2

TL;DR

This paper reports the experimental discovery of type II Weyl semimetal states in MoTe2, characterized by unique Fermi arc states and Lorentz invariance violation, confirmed through spectroscopy and theoretical calculations.

Contribution

The study provides the first direct observation of Fermi arc states in MoTe2, establishing it as a type II Weyl semimetal with unique topological properties.

Findings

Identification of Fermi arc states in MoTe2

Consistency with first-principles calculations

Confirmation of Lorentz invariance violation in Weyl fermions

Abstract

A new type of Weyl semimetal state, in which the energy values of Weyl nodes are not the local extrema, has been theoretically proposed recently, namely type II Weyl semimetal. Distinguished from type I semimetal (e.g. TaAs), the Fermi surfaces in a type II Weyl semimetal consist of a pair of electron and hole pockets touching at the Weyl node. In addition, Weyl fermions in type II Weyl semimetals violate Lorentz invariance. Due to these qualitative differences distinct spectroscopy and magnetotransport properties are expected in type II Weyl semimetals. Here, we present the direct observation of the Fermi arc states in MoTe2 by using angle resolved photoemission spectroscopy. Two arc states are identified for each pair of Weyl nodes whoes surface projections of them possess single topological charge, which is a unique property for type II Weyl semimetals. The experimentally determined Fermi arcs are consistent with our first principle calculations. Our results unambiguously establish that MoTe2 is a type II Weyl semimetal, which serves as a great test bed to investigate the phenomena of new type of Weyl fermions with Lorentz invariance violated.