Quasiparticle Gap Renormalization Driven by Internal and External Screening in a WS_{2} Device.

The electronic band gap of a two-dimensional semiconductor within a device architecture is sensitive to variations in screening properties of adjacent materials in the device and to gate-controlled doping. Here, we employ microfocused angle-resolved photoemission spectroscopy to separate band gap renormalization effects stemming from environmental screening and electron doping during in situ gating of a single-layer WS_{2} device. The WS_{2} is supported on hexagonal boron nitride and contains a section that is exposed to vacuum and another section that is encapsulated by a graphene contact. We directly observe the doping-induced semiconductor-metal transition and band gap renormalization in the two sections of WS_{2}. Surprisingly, a larger band gap renormalization is observed in the vacuum-exposed section than in the graphene-encapsulated-and thus ostensibly better screened-section of the WS_{2}. Using GW calculations, we determine that intrinsic screening due to stronger doping in vacuum-exposed WS_{2} exceeds the external environmental screening in graphene-encapsulated WS_{2}.