Insulating Bulk State in Monolayer WTe₂

The layered semimetal WTe₂ displays a diverse set of properties in the two-dimensional limit. For example, using an electrostatic gate, one can control the carrier density and change the state of monolayer WTe₂ from a 2D topological insulator a 2D superconductor. We will discuss our recent work to better understand the properties of the insulating bulk state seen in monolayer WTe₂ near charge neutrality. Using graphene as a probe of the transverse penetrating electric field, we determine the chemical potential as a function of charge density, finding a thermodynamic gap of 45±5 meV at low temperatures. We relate the measurements to transport and angle-resolved photoemission measurements.