Lattice Phonon-Mediated Exciton-Surface Plasmon Polariton Scattering in Monolayer MoS₂–Gold Hybrid Nanostructure

We investigate lattice phonon-mediated scattering in the presence of strong light-matter interaction between excitons in monolayer MoS2 and propagating surface plasmon polaritons (SPPs) at the gold–MoS2 interface at room temperature. The strong radiative exciton–SPP interaction results in characteristic anticrossing in dispersion relation of the hybrid nanostructure at both A and B excitons of monolayer MoS2. The exciton–SPP polariton formation is probed by angle-resolved coherent scattering as well as photoluminescence spectroscopy of the hybrid nanostructure in the Kretschmann configuration and rationalized within the coupled oscillator framework. The phonon-mediated polariton scattering is explored by angle-resolved Raman spectroscopy under resonant excitation conditions. The exciton–SPP polariton Raman spectrum reveals considerable enhancement and broadening, particularly in two-phonon modes involving intervalley scattering accompanied by blue shift of the E2 mode. The pronounced changes are suggestive of higher polariton–phonon interaction cross sections and induced strain. The nonradiative relaxation of the hybrid polariton modes results in hot-electron transfer to monolayer MoS2 that induces compressive strain due to its piezoelectric nature. Our experimental results shed light on the relationship between exciton–SPP interaction, charge transfer, and mechanical strain in metal–semiconductor hybrid nanostructures and demonstrate an innovative all-optical approach to engineer the optical, electronic, and mechanical properties of 2D semiconductors.