/graphene heterostructures

The strong Coulomb interaction between charge carriers in atomically thin transition metal dichalcogenides (e.g. MoS₂, WSe₂) is sensitive to the nearby dielectric environment. Here, we investigate the optical response of monolayer WSe₂, which is in contact with gate-tunable graphene in van der Waals heterostructures, by optical reflection spectroscopy. We find that both the exciton binding energy and quasiparticle bandgap of WSe₂can be renormalized by the dielectric screening effect. The effect can also be modulated upon the formation of Landau levels in graphene under perpendicular magnetic fields. Furthermore, we directly observe inter-band Landau level transitions of WSe₂, which helps to accurately determine the quasiparticle bandgap and effective cyclotron mass in WSe₂ as a function of dielectric screening.