Dynamic control of nonlinear emission by exciton-photon coupling in WS₂ metasurfaces

Transition metal dichalcogenides are promising quantum materials because of unique exciton-photon interactions. These interactions can be enhanced by coupling with resonant photonic structures, especially in the nonlinear light emission processes like second-harmonic generation (SHG). However, excitonic absorption may dampen SHG. Here, we demonstrate tunable SHG enhancement using virtual coupling effects between quasi-bound state in the continuum (qBIC) optical resonances and tunable excitons in high-index WS₂ metasurfaces with crescent meta-atoms. These metasurfaces promote a magnetic-type qBIC resonance, enabling control over nonlinear optical processes in the visible spectrum. The used qBIC resonance at half the exciton energy increases SHG efficiency by 98-fold compared to monolayer WS₂ and by four orders of magnitude relative to an unpatterned WS₂ film. The enhancement is tunable with temperature and incident light polarization, allowing the dynamic control of virtual coupling and SHG efficiency, thereby paving the way for next-generation reconfigurable metaoptics devices.