Why matter matters: importance of inter-site coupling and disorder in polariton transport

Understanding light-matter interactions is pivotal for advancing photonic technologies. Exciton-polaritons (EPs) — hybrid light-exciton states often formed by embedding molecules and materials in optical cavities — have gained significant attention due to their unique blend of properties: strong nonlinearity from the exciton component and low effective mass with high coherence from the photon component. The highly delocalized nature of EPs enables long-range energy transport. EP transport properties are inferred from their dispersion relation, with all dispersive properties inherited from the photonic fraction of the polariton. As such, intrinsic molecular or material properties are typically thought to play a negligible role in EP transport. Here, we challenge this assumption by systematically characterizing EP transport in systems with varied excitonic (inter-site) coupling and disorder through spatiotemporally-resolved microscopy. By comparing EP transport in systems ranging from delocalized Wannier-Mott excitons in crystalline 2D perovskites to localized Frenkel excitons in amorphous molecular systems, we show that EP properties are intrinsically linked to exciton-phonon interaction strength, inter-site coupling, and energetic and orientational disorder of the underlying matter. Our work emphasizes the importance of choosing the matter component of polaritons with care for any given application.