Moiré Phonons and Emergent Exciton-Phonon Coupling in a Moiré Heterobilayer

Moir\'e superlattices have emerged as a new platform for engineering electronic and optical properties in van der Waals heterostructures, enabling control over correlated and excitonic phenomena. Yet the impact of moir\'e superlattices on exciton-phonon coupling remains largely unexplored. Here we demonstrate emergent, layer-selective coupling between moir\'e phonons and moir\'e excitons in angle-aligned WS2/WSe2 heterobilayers. Using a broadband terahertz phonon transducer, we coherently launch moir\'e phonons that resonantly perturb the excitonic states. We show that the exciton-phonon coupling is intrinsically modified by the moir\'e superlattice in a layer-selective manner. A driven oscillator model captures the dynamics, revealing three moir\'e phonon resonances with distinct coupling to the moir\'e excitons. First principles calculations show that many moir\'e phonon modes can arise with distinct strongly hybridized in-plane and out-of-plane vibrations in the moir\'e unit cells. The calculations further identify the three experimentally observed moir\'e phonons and their emergent characteristic coupling to the moir\'e excitons.