Tunable Excitons in Rhombohedral Trilayer Graphene

Rhombohedral stacked multilayer graphene is a unique material where the bandgap can be continuously tuned by an out-of-plane electric field. It hosts excitons with unconventional optical selection rule and provides a novel platform to study exciton physics in the context of valley pseudospin and band topology. We observed tunable exciton states in rhombohedral trilayer graphene via a photocurrent spectroscopy technique. Unlike in AB-stacked bilayer graphene, the optical spectrum of rhombohedral trilayer graphene is dominated by exciton p and d states, while the s exciton state becomes completely dark. This observation is a direct consequence of the pseudospin texture near the band extrema. I will also discuss the moire effects on the exciton physics in a trilayer graphene/hBN superlattice.