Investigations into the nature of edge conduction in monolayer WTe₂

Monolayer WTe₂ displays edge conduction that is consistent with the material being a two-dimensional topological insulator, where the current is confined to helical edge modes while the interior region is insulating. The helical nature of the edge conduction should limit the conductance between adjacent contacts on an edge to e²/h, and this is consistent with experiments to date. However, the helical nature has not been supported by experiments that probe the spin properties of the edge states, and the reason the conductance is always less than e²/h is not yet established. To address this, we investigate the dependence on magnetic field orientation of the conduction of edges and cracks in monolayer WTe₂ flakes as a function of gate voltage, temperature, and edge direction relative to the crystal axes. Most importantly, we find that the conductance is suppressed by the component of the field perpendicular to a particular axis in the crystal. A theoretical model of the bands accounting for the crystal symmetries is consistent with this being the spin axis, implying a very simple form for the spin-orbit coupling in this material.