# Ubiquitous formation of bulk Dirac cones and topological surface states from a single orbital manifold in transition-metal dichalcogenides

## TL;DR

This paper reveals that transition-metal dichalcogenides naturally host bulk Dirac fermions and topological surface states originating from a single p-orbital manifold, broadening the understanding of their electronic properties.

## Contribution

It demonstrates the universal emergence of Dirac cones and topological states in TMDs from a single orbital, based on density functional theory and photoemission studies.

## Key findings

- Existence of bulk Dirac fermions in six TMDs
- Topological surface states arise from a single p-orbital manifold
- These states are linked to a trigonal crystal field

## Abstract

Transition-metal dichalcogenides (TMDs) are renowned for their rich and varied properties. They range from metals and superconductors to strongly spin-orbit-coupled semiconductors and charge-density-wave systems, with their single-layer variants one of the most prominent current examples of two-dimensional materials beyond graphene. Their varied ground states largely depend on the transition metal d-electron-derived electronic states, on which the vast majority of attention has been concentrated to date. Here, we focus on the chalcogen-derived states. From density-functional theory calculations together with spin- and angle- resolved photoemission, we find that these generically host type-II three-dimensional bulk Dirac fermions as well as ladders of topological surface states and surface resonances. We demonstrate how these naturally arise within a single p-orbital manifold as a general consequence of a trigonal crystal field, and as such can be expected across a large number of compounds. Already, we demonstrate their existence in six separate TMDs, opening routes to tune, and ultimately exploit, their topological physics.