Electrically Tunable Strong Exciton Resonance of Second Harmonic Generation in van der Waals Heterostructures

Nanomaterials with strong and tunable nonlinear responses have lots of applications and are always being sought. Two-dimensional (2D) transition metal dichalcogenides (TMDs) materials are emerging candidates with strong second-order nonlinearity. However, methods to efficiently tune their second-order optical nonlinearity remain challenging. Herein, a new method to efficiently tune the second-order nonlinear response from monolayer TMDs within van der Waals heterostructures (vdWHs) electrically is demonstrated. Dynamic tuning of the local second-harmonic generation (SHG) up to 100% in a graphene/h-BN/WSe2 heterostructures corresponding to a tuning efficiency of approximate to 12.5% per volt is realized, benefitting from the strong exciton resonance. Furthermore, the long-standing issue that how the interfacial carrier transfer and exciton resonance affect the nonlinear response of TMDs within van der Waals heterostructures at the same time is figured out by control experiments and theoretical calculation. The work will pave a new way for constructing efficient on-chip nonlinear optoelectronic devices based on TMDs and strengthen the understanding of excitonic dynamics in 2D materials.