Nonlinear valley phonon scattering under the strong coupling regime

Research efforts of cavity quantum electrodynamics have focused on the manipulation of matter hybridized with photons under the strong coupling regime 1 – 3 . This has led to striking discoveries including polariton condensation 2 and single-photon nonlinearity 3 , where the phonon scattering plays a critical role 1 – 9 . However, resolving the phonon scattering remains challenging for its non-radiative complexity. Here we demonstrate nonlinear phonon scattering in monolayer MoS 2 that is strongly coupled to a plasmonic cavity mode. By hybridizing excitons and cavity photons, the phonon scattering is equipped with valley degree of freedom and boosted with superlinear enhancement to a stimulated regime, as revealed by Raman spectroscopy and our theoretical model. The valley polarization is drastically enhanced and sustained throughout the stimulated regime, suggesting a coherent scattering process enabled by the strong coupling. Our findings clarify the feasibility of valley–cavity-based systems for lighting, imaging, optical information processing and manipulating quantum correlations in cavity quantum electrodynamics 2 , 3 , 10 – 17 . Strong exciton–polariton coupling is leveraged as a means to open up phonon scattering channels that are otherwise weak.