Imaging Conductive Edge States in Monolayer WTe2

The quantum spin Hall (QSH) effect occurs in two-dimensional topological insulators where helical edge states circulate the insulating bulk. Recent experiments have reported QSH signatures in monolayer WTe2. In our experiment, we use microwave impedance microscopy (MIM), a scanning probe technique that senses materials’ local electrical properties, to directly image the edge states in monolayer WTe2, and correlate their behaviors with electrical transport. Conductive states are clearly resolved at edges of the monolayer WTe2. They remain conductive when the bulk carrier density is tuned through the bandgap, but become only slightly weaker at high magnetic field while the conductance measured by transport is strongly suppressed. The edge conduction can be resolved up to 100 K in temperature when the bulk becomes conductive. In addition, we also observe conduction features in the bulk of the WTe2 flake. We will discuss the implications of these observations on the topological properties of monolayer WTe2.