Gate tuneable ultrafast charge transfer in graphene/MoS2 heterostructures

We report ultrafast pump-probe measurements on a graphene/MoS 2 heterostructure and demonstrate sub picosecond exciton dissociation and charge transfer from MoS 2 to graphene, one order of magnitude faster than in type II two-dimensional heterostructures [1]. The process can be controlled by applying an external gate and shifting the Fermi level of graphene. For pump-probe measurements we excite the gate controlled graphene/MoS 2 heterostructure at 400 nm, well above the MoS 2 bandgap [2], and probe the normalized differential transmission changes (ΔΤ/T) of the M0S 2 first exciton (A exciton) at 660nm with time resolution∼200fs. In this configuration, MoS2 acts as the absorbing material for visible wavelengths while graphene is the electron scavenger [3], as depicted in Fig. 1.