Probing the bulk electronic states in monolayer WTe2 using impedance and potential measurements

The layered semimetal WTe2 in the monolayer limit behaves as a two-dimensional topological insulator with a bulk gap and conducting edge states. However, the nature of this bulk gap is unclear. Recent measurements suggest it may be an excitonic insulator. To investigate this question, we combine scanning microwave impedance microscopy (MIM), Kelvin probe force microscopy (KPFM), and capacitance measurements on monolayer WTe2 devices. MIM probes the local conductivity; KPFM measures the local chemical potential; and quantum capacitance is associated with the electronic density of states. We measure these quantities as a function of carrier density, magnetic field, and temperature. By correlating these measurements, we will discuss their implications on the bulk electronic structure in monolayer WTe2.