Interlayer\nExciton–Phonon Coupling in MoSe<sub>2</sub>/WSe<sub>2</sub> Heterostructures

Transition metal dichalcogenide heterostructures have\ngarnered\nstrong interest for their robust excitonic properties, mixed light–matter\nstates such as exciton-polaritons, and tailored properties, vital\nfor advanced device engineering. Two-dimensional heterostructures\ninherit their physics from monolayers with the addition of interlayer\nprocesses that have been particularly emphasized for their electronic\nand optical properties. Here, we demonstrate the interlayer coupling\nof the MoSe<sub>2</sub> phonons to WSe<sub>2</sub> excitons in a WSe<sub>2</sub>/MoSe<sub>2</sub> heterostructure using resonant Raman scattering.\nThe WSe<sub>2</sub> monolayer induces an interlayer resonance in the\nRaman cross-section of the MoSe<sub>2</sub> A<sub>1g</sub> phonons.\nFrozen-phonon calculations within density functional theory reveal\na strong deformation-potential coupling between the A<sub>1g</sub> MoSe<sub>2</sub> phonon and the electronic states of the close-by\nWSe<sub>2</sub> layer approaching 20% of the intralayer coupling to\nthe MoSe<sub>2</sub> electrons. Understanding the vibrational properties\nof van der Waals heterostructures requires going beyond the sum of\ntheir constituents and considering cross-material coupling.