Exciton delocalization suppresses polariton scattering

Abstract

Exciton-polaritons (EPs) are hybrid light-matter quasiparticles that combine exciton-mediated nonlinearities with long-range coherence, ideal for energy harvesting and nonlinear optics. Optimizing EPs is predicated on a still-elusive understanding of how disorder affects their propagation and dephasing times. Here, using cutting-edge femtosecond spatiotemporal microscopy, we image EP propagation in two-dimensional semiconductors, molecular crystals, and amorphous molecular films with systematically varied exciton-phonon coupling, exciton delocalization, and static disorder. Despite possessing similar EP dispersions, we observe dramatically different transport velocities and scattering times across systems. We establish a robust scaling law linking EP scattering to exciton transfer integral, demonstrating that polaritons based on materials with large exciton bandwidths are protected against disorder even for highly excitonic EPs. This observation cannot be deduced from the systems’ linear optical properties. Our work highlights the critical role of the matter component in dictating polariton properties and provides precise guidelines for simultaneously optimizing EP propagation and nonlinearities.