# Spontaneous breaking of time-reversal symmetry at the edges of 1T' monolayer transition metal dichalcogenides

## TL;DR

This paper demonstrates the existence of magnetic, gapless edge states with broken time-reversal symmetry in 1T' monolayer transition metal dichalcogenides, and shows these states are robust under electric fields, impacting their use in quantum spin Hall devices.

## Contribution

It provides first-principles evidence of magnetic edge states with broken time-reversal symmetry in 1T' TMDs and confirms the robustness of topological edge states under electric fields.

## Key findings

- Magnetic edge states are present on 1T' TMD edges.
- These edge states are gapless and break time-reversal symmetry.
- Topological edge states can be switched off by an electric field, but magnetic states remain robust.

## Abstract

Using density functional theory calculations and the Greens's function formalism, we report the existence of magnetic edge states with a non-collinear spin texture present on different edges of the 1T' phase of the three monolayer transition metal dichalcogenides (TMDs): MoS$_2$, MoTe$_2$ and WTe$_2$. The magnetic states are gapless and accompanied by a spontaneous breaking of the time-reversal symmetry. This may have an impact on the prospects of utilizing WTe$_2$ as a quantum spin Hall insulator. It has previously been suggested that the topologically protected edge states of the 1T' TMDs could be switched off by applying a perpendicular electric field. We confirm with fully self-consistent DFT calculations, that the topological edge states can be switched off. The investigated magnetic edge states are seen to be robust and remains gapless when applying a field.