Giant Modulation of Second-Harmonic Generation in CuInP₂S₆ by Interfacing with MoS₂ Atomic Layers

Probing and manipulating the intriguing nonlinear optical responses in van der Waals (vdW) ferroelectrics offer opportunities for their applications in nanophotonics. Here, we report the observation of giant and tunable second-harmonic generation (SHG) in ferroelectric CuInP₂S₆ (CIPS) and CIPS/MoS₂ heterostructures. The results show that CIPS, ranging from multilayer to bulk-like samples, all exhibit strong SHG with giant anisotropy. The SHG anisotropy is attributed to the local strain along the <i>a</i>-axis that naturally exists in CIPS, as evidenced by piezoresponse force microscopy measurement. We further realized the strong modulation of SHG in CIPS by interfacing with monolayer MoS₂. A combination of polarization, temperature, and thickness-dependent SHG and photoluminescence analyses shows that the nonlinear optical signal control in CIPS/MoS₂ heterostructures is unrelated to the polar symmetry of CIPS and MoS₂ but is driven by light absorption-mediated interfacial coupling. Our study provides a material platform based on vdW ferroelectric heterostructures for achieving dynamic control of nonlinear optical responses, which shows great potential applications in modern nanophotonics.