# The influence of lattice termination on the edge states of the quantum spin Hall insulator monolayer $1T'$-WTe$_2$

## TL;DR

This study investigates how different sample terminations affect the electronic edge states and conductance in monolayer $1T'$-WTe$_2$, revealing the impact of edge quality and magnetic fields on quantum spin Hall properties.

## Contribution

We developed a minimal tight-binding model incorporating spin-orbit coupling and symmetry, and analyzed how edge termination influences edge states and conductance in monolayer $1T'$-WTe$_2$.

## Key findings

- Edge Dirac point often buried in bulk bands due to electron-hole asymmetry.
- Magnetic field opens a Zeeman gap, suppressing conductance when the Dirac point is in the gap.
- Edge disorder significantly reduces conductance across the bulk gap regardless of edge orientation.

## Abstract

We study the influence of sample termination on the electronic properties of the novel quantum spin Hall insulator monolayer $1T'$-WTe$_2$. For this purpose, we construct an accurate, minimal 4-orbital tight-binding model with spin-orbit coupling by employing a combination of density-functional theory calculations, symmetry considerations, and fitting to experimental data. Based on this model, we compute energy bands and 2-terminal conductance spectra for various ribbon geometries with different terminations, with and without magnetic field. Because of the strong electron-hole asymmetry we find that the edge Dirac point is buried in the bulk bands for most edge terminations. In the presence of a magnetic field, an in-gap edge Dirac point leads to exponential suppression of conductance as an edge Zeeman gap opens, whereas the conductance stays at the quantized value when the Dirac point is buried in the bulk bands. Finally, we find that disorder in the edge termination drastically changes this picture: the conductance of a sufficiently rough edge is uniformly suppressed for all energies in the bulk gap regardless of the orientation of the edge.