Electric Field Tunable Interlayer Relaxation Process and Interlayer Coupling in WSe2/Graphene Heterostructures

Transition metal dichalcogenides van der Waals (vdWs) heterostructures present fascinating optical and electronic phenomena, and bear tremendous significance for electronic and optoelectronic applications. As the significant merits in vdWs heterostructures, the interlayer relaxation of excitons and interlayer coupling at the heterointerface reflect the dynamic behavior of charge transfer and the coupled electronic/structural characteristics, respectively, which may give rise to new physics induced by quantum coupling. In this work, upon tuning the photoluminescence (PL) properties of WSe2/graphene and WSe2/MoS2/graphene heterostructures by virtue of electric field, it is demonstrated that the interlayer relaxation of excitons at the heterointerface in WSe2/graphene, which is even stronger than that in MoS2/graphene and WSe2/MoS2 , plays a dominant role in PL tuning in WSe2/graphene, while the carrier population in WSe2 induced by electric field has a minor contribution. In addition, it is discovered that the interlayer coupling between monolayer WSe2 and graphene is enhanced under high electric field, which breaks the momentum conservation of first order Raman-allowed phonons in graphene, yielding the enhanced Raman scattering of defects in graphene. The interplay between electric field and vdWs heterostructures may provide versatile approaches to tune the intrinsic electronic and optical properties of the heterostructures.