Photoluminescence quenching and spin-orbit coupling in graphene/WSe₂ heterostructure

Strong spin-orbit coupling (SOC) can be introduced into graphene by putting transition metal dichalcogenides (TMDs) like WSe₂ onto graphene. Due to the proximity effect, graphene can inherit the strong SOC from TMDs. We find the strength of the acquired SOC depends on the stacking order of the heterostructures when we use boron nitride (BN) as the capping layer, i.e., SiO₂/graphene/WSe₂/BN exhibits a stronger SOC in graphene than SiO₂/WSe₂/graphene/BN. We utilize photoluminescence (PL) to characterize the interaction between WSe₂ and graphene by investigating the PL quenching of monolayer chemical vapor deposition grown WSe₂ in these two stacks. We observe much stronger PL quenching in the graphene/WSe₂/BN stack than in the WSe₂/graphene/BN stack. We attribute the much reduced PL quenching in the latter stack to the increased interlayer distance between graphene and WSe₂. Consequently, we see a strong WAL effect in the former stack but a small or vanished WAL in the latter one. Our observations and hypothesis are further supported by first principles calculations, which show a clear difference in the interlayer distance between graphene and WSe₂ of these two stacks and therefore the resulting SOC strength.