Interlayer Exciton-Phonon Coupling in MoSe₂/WSe₂ Heterostructures

Transition metal dichalcogenide heterostructures have garnered strong interest for their robust excitonic properties, mixed light-matter states such as exciton-polaritons, and tailored properties, vital for advanced device engineering. Two-dimensional heterostructures inherit their physics from monolayers with the addition of interlayer processes that have been particularly emphasized for their electronic and optical properties. Here, we demonstrate the interlayer coupling of the MoSe₂ phonons to WSe₂ excitons in a WSe₂/MoSe₂ heterostructure using resonant Raman scattering. The WSe₂ monolayer induces an interlayer resonance in the Raman cross-section of the MoSe₂ A_1g phonons. Frozen-phonon calculations within density functional theory reveal a strong deformation-potential coupling between the A_1g MoSe₂ phonon and the electronic states of the close-by WSe₂ layer approaching 20% of the intralayer coupling to the MoSe₂ electrons. Understanding the vibrational properties of van der Waals heterostructures requires going beyond the sum of their constituents and considering cross-material coupling.