Edge conduction in monolayer WTe2

TL;DR

This study demonstrates that monolayer WTe2 exhibits edge conduction consistent with a two-dimensional topological insulator, showing insulating bulk and edge-specific conductance suppressed by magnetic fields.

Contribution

It provides experimental evidence that monolayer WTe2 can act as a 2DTI with edge conduction, a novel finding for this material.

Findings

Monolayer WTe2 becomes insulating in the bulk below 100 K.

Edge conduction persists and is suppressed by magnetic fields.

Observed edge conductance is below the quantized value.

Abstract

A two-dimensional topological insulator (2DTI) is guaranteed to have a helical 1D edge mode in which spin is locked to momentum, producing the quantum spin Hall effect and prohibiting elastic backscattering at zero magnetic field. No monolayer material has yet been shown to be a 2DTI, but recently the Weyl semimetal WTe2 was predicted to become a 2DTI in monolayer form if a bulk gap opens. Here, we report that at temperatures below about 100 K monolayer WTe2 does become insulating in its interior, while the edges still conduct. The edge conduction is strongly suppressed by in-plane magnetic field and is independent of gate voltage, save for mesoscopic fluctuations that grow on cooling due to a zero-bias anomaly which reduces the linear-response conductance. Bilayer WTe2 also becomes insulating at low temperatures but does not show edge conduction. Many of these observations are consistent with monolayer WTe2 being a 2DTI. However, the low temperature edge conductance, for contacts spacings down to 150 nm, is below the quantized value,