Direct measurement of monolayer WSe₂chemical potential

Thermodynamic properties of electronic materials can provide unique insight into the band structure and electron interaction effects. We investigate the chemical potential of monolayer WSe₂ using an independently contacted double layer structure where the top layer consists of monolayer WSe₂, and the bottom layer is a monolayer graphene gate. In addition, the double layer structure has top and bottom gates, to control the densities in the WSe₂ and monolayer graphene, respectively. This device structure enables direct chemical potential measurements by using graphene back gate as a resistively detected Kelvin probe. Indeed, by tracking the charge neutrality point of the graphene gate as a function of interlayer voltage and top gate voltage, which in turn controls the WSe₂ layer carrier density we are able to directly measure the WSe₂ layer chemical potential over a wide range of doping densities in the valence and conduction bands, as well as across the bandgap. Remarkably, our measurements are also able to access the WSe₂ monolayer chemical potential in the highly insulating regime at low doping concentrations.