Intermaterial Hybridization as a Mechanism for Tunable Second-Harmonic Generation in Quantum Dot-Monolayer MoS2 Systems.

Coherent hybridization between distinct material systems can fundamentally reshape the optical response, yet its quantitative influence on nonlinear susceptibility has remained largely unexplored. Here, we demonstrate that coherent coupling between CdSe-based quantum dots and monolayer MoS2 governs second-harmonic generation (SHG), giving rise to both a pronounced non-monotonic distance dependence and orders of magnitude enhancement in SHG intensity. By systematically tuning the interfacial separation, we uncovered a robust non-monotonic evolution of the SHG. This behavior cannot be explained by previously suggested incoherent mechanisms such as energy transfer or charge transfer, which predict strictly monotonic scaling and fail to account for the dramatic amplification observed. First-principles calculations reveal substantial conduction-band wave function delocalization across the heterogeneous interface, providing microscopic evidence of coherent electronic hybridization. Guided by this insight, we developed a rigorous intermaterial coherent hybridization (ICH) model in which the SHG response is governed by the mixing angle of hybridized eigenstates. The ICH model accurately reproduces both the non-monotonic distance dependence and the large enhancement of SHG without invoking dominant incoherent processes, establishing a deterministic hybridization framework for second-order nonlinear susceptibility at material interfaces. These results identify coherent electronic hybridization as a universal route for engineering a nonlinear optical response beyond intrinsic material limits, offering a new paradigm for interfacial nonlinear photonics.