Electrical Signatures of Interfacial Charge Transfer Enabling Second-Harmonic Generation in Centrosymmetric Bilayer...

Optical nonlinearity in two-dimensional (2D) materials underpins a wide range of photonic and quantum technologies, yet second-order nonlinearity is symmetry-forbidden in centrosymmetric systems, unless the inversion symmetry is broken by external factors or interfacial effects. Although interfacial charge transfer in 2D heterostructures is widely inferred to induce second-order nonlinear responses, electrical signatures linking emergent nonlinearity to charge redistribution remain elusive. Here, we report the activation of second-harmonic generation (SHG) in centrosymmetric bilayer 2H-MoTe₂ via interfacial coupling with anisotropic NbOCl₂. By employing a field-effect transistor configuration in which both source and drain electrodes are deliberately placed on the MoTe₂ layer, we isolate lateral channel transport from interfacial coupling, enabling direct electrical probing of interfacial charge transfer. Optical and electrical measurements reveal that charge-transfer-induced charge redistribution breaks the inversion symmetry of MoTe₂, thereby generating an effective second-order polarization. Furthermore, we show that SHG anisotropy in bilayer MoTe₂ exhibits decoupling from the principal axis of NbOCl₂, reflecting interlayer screening and modified symmetry transfer. This work establishes an electrical link between interfacial charge redistribution and nonlinear optical response in centrosymmetric 2D materials, providing insights for designing electrically tunable nonlinear photonic devices and integrated quantum light sources based on layered heterostructures.