Resonant Raman\nScattering of Surface Phonon Polaritons\nMediated by Excitons in WSe<sub>2</sub> Films

Surface phonon polaritons\npropagating along interfaces of polar\ndielectrics coexist with excitons in many van der Waals heterostructures,\nso understanding their mutual interactions is of great interest. Here,\nwe investigate the contribution of type I surface phonon polariton\n(SPhP) of hBN to the low-temperature resonant-Raman spectra of hBN/WSe<sub>2</sub> heterostructures. When the laser energy is such that the\nscattered photons have energy close to that of the WSe<sub>2</sub> excitons, the resonantly enhanced Raman signal enables the characterization\nof even one monolayer-thick hBN. We are able to explain the signal\nusing transfer matrix method simulations of SPhP dispersions, provided\nthat we assume the Raman scattering to be momentum nonconserving,\nas could be the case if localized WSe<sub>2</sub> exciton states participated\nin the process. However, we cannot exclude the contribution of the\nTO and ZO phonons to the measured signal. We further show that resonant\nRaman scattering from SiO<sub>2</sub> SPhP can also be mediated by\nWSe<sub>2</sub>.