Second Harmonic Generation in van der Waals Heterostructure of Centrosymmetric ReS2 and Graphene

Van der Waals (vdW) heterostructures of two-dimensional (2D) materials promise exotic properties beyond the reach of existing material systems and open unprecedented opportunities for device applications. Here, it is demonstrated that vdW stacking of centrosymmetric ReS2 and graphene into heterostructure could induce strong second harmonic generation (SHG), though there is not any SHG from the individual ReS2 or graphene. It could be attributed to the interfacial charge transfer in the heterostructure. With the distorted 1T crystal structure of ReS2 and electrostatic screening effect, the charge transfer gives rise to non-uniform charge distribution across the ReS2's atomic layers, resulting in the broken centrosymmetry for the second-order hyperpolarizability. At the specific pump wavelength of 1550 nm, the strength of the induced SHG in a trilayer ReS2/graphene vdW heterostructure is approximately twice of that from a monolayer MoS2. This work reveals vdW stacking is a simple and efficient method for inducing SHG in 2D materials with centrosymmetry, which could be considered as another unique attribute of 2D materials. It also indicates that SHG spectroscopy is a valid technique for probing charge transfer and distribution in heterostructures of 2D materials.