Tilted Dirac Fermions

TL;DR

This paper introduces a new class of topological semimetals in 2D nonsymmorphic crystals, specifically in monolayer MTe2, characterized by tilted Dirac cones and topological properties, with implications for magnetoresistance and photoemission.

Contribution

It presents the concept of band-inverted topological semimetals in 2D nonsymmorphic crystals and characterizes their Dirac band touching topologically using Wilson loops, supported by first-principles calculations.

Findings

Identification of tilted Dirac cones in monolayer MTe2.

Topological characterization of Dirac band touchings.

Connection to non-saturating magnetoresistance in WTe2.

Abstract

We introduce the notion of a band-inverted, topological semimetal in two-dimensional nonsymmorphic crystals. This notion is materialized in the monolayers of MTe$_2$ (M $=$ W, Mo) if spin-orbit coupling is neglected. We characterize the Dirac band touching topologically by the Wilson loop of the non-Abelian Berry gauge field. An additional feature of the Dirac cone in monolayer MTe$_2$ is that it tilts over in a Lifshitz transition to produce electron and hole pockets, a type-II Dirac cone. These pockets, together with the pseudospin structure of the Dirac electrons, suggest a unified, topological explanation for the recently-reported, non-saturating magnetoresistance in WTe$_2$, as well as its circular dichroism in photoemission. We complement our analysis and first-principle bandstructure calculations with an $\textit{ab-initio}$-derived-derived tight-binding model for the WTe$_2$ monolayer.