Second-Harmonic Generation in 2D Heterostructures Strongly Modulated by Interlayer Coupling

Second-harmonic generation (SHG) is a nonlinear optical process where two photons with the same energy convert into a new photon with twice the energy. Transition metal dichalcogenides (TMDs) have been spotlighted for their high SHG efficiency and atomic thickness circumventing the phase-matching requirement. Combinatorial stacking of TMDs also enables the fabrication of heterostructures with desired nonlinear optical properties. In this work, we report that interlayer coupling dramatically affects the SHG response of individual monolayers in MoSe₂/WS₂. We were able to selectively probe each monolayer of the heterostructure using polarization-resolved detection, which revealed SHG intensity and phase were remarkably different in hetero-stack regions compared to unstacked monolayers. The modulation of the former reached a maximum when the photon energy matched with the exciton resonance of the adjacent layer. The nature of the interlayer coupling will be discussed.