Gating and superlattice effects in monolayer WSe₂ devices in micro-ARPES

We investigate the effects of electrostatic doping and moiré superlattice potentials on monolayer WSe₂ using micro-angle-resolved photoemission spectroscopy (micro-ARPES). By employing a local back gate of thin graphite under a hexagonal boron nitride dielectric support, we electrostatically populate the WSe₂ conduction band during the photoemission measurements. We find the conduction band edge to be at the zone corner, or K point, confirming the direct gap nature of this material and yielding a measurement of the single-particle gap. As the electron doping is increased to a maximum of ~1.4E13 cm^-2 the valence band shifts upwards towards the conduction band, corresponding to substantial band gap renormalization. At the highest doping levels, the conduction band minimum at the lower symmetry Q point is also populated, showing that it is within ∼30 meV of the minimum at K. In some devices we also observe folded copies of the hBN and WSe₂ bands with intensities often comparable to the original bands, yielding information about moire superlattice effects.