Role of Coherence in Polarization Response of Hybrid Monolayer MoS ₂ ‐Gold Nanoparticle Systems

Monolayers of transition metal dichacogenides (1L‐TMDs) show strong second‐order nonlinearity and symmetry‐driven selection rules from their threefold lattice symmetry. This process resembles the valley‐contrasting selection rules for photoluminescence (PL) in these materials. However, the underlying physical mechanisms fundamentally differ since second harmonic generation (SHG) is a coherent process, whereas PL is incoherent, leading to distinct interactions with photonic nanoresonators. In this study, the far‐field circular polarization properties of SHG from MoS 2 monolayers resonantly interacting with spherical gold nanoparticles were investigated. The results indicate that the coherence of the second harmonic allows its polarization to be mostly preserved, unlike in an incoherent process, where the polarization is scrambled. These findings provide important insights for future applications in valleytronics and quantum nanooptics, where both coherent and incoherent processes can be probed in such hybrid systems without altering sample geometry or operational wavelength.