Exciton Delocalization Suppresses Polariton Scattering

Exciton–polaritons (EPs) are hybrid light–matter quasiparticles that merge the long-range coherence of photons with the nonlinear and electronic functionalities of excitons. Understanding how disorder influences their propagation and dephasing remains a major challenge for realizing efficient polaritonic devices. Using femtosecond spatiotemporal microscopy, we directly visualize EP transport across molecular crystals, amorphous molecular films, and two-dimensional semiconductors exhibiting systematically varied exciton–phonon coupling, exciton delocalization, and static disorder. Despite showing similar EP dispersions, these systems display markedly different transport velocities and scattering times. In this talk, we propose a universal scaling relation linking polariton scattering to the exciton transfer integral, demonstrating that materials with larger exciton bandwidths are inherently protected against disorder, even for highly excitonic EPs. This behavior cannot be predicted from linear optical spectra alone. Our results reveal that the matter component critically governs EP coherence and provide a quantitative framework for designing disorder-resilient, long-range coherent polaritonic systems.