Long-Range Ballistic Propagation of 80% Excitonic\nFraction Polaritons in a Perovskite Metasurface at Room Temperature

Exciton-polaritons,\nhybrid light-matter excitations arising from\nthe strong coupling between excitons in semiconductors and photons\nin photonic nanostructures, are crucial for exploring the physics\nof quantum fluids of light and developing all-optical devices. Achieving\nroom temperature propagation of polaritons with a large excitonic\nfraction is challenging but vital, e.g., for nonlinear light transport.\nWe report on room temperature propagation of exciton-polaritons in\na metasurface made from a subwavelength lattice of perovskite pillars.\nThe large Rabi splitting, much greater than the optical phonon energy,\ndecouples the lower polariton band from the phonon bath of the perovskite.\nThese cooled polaritons, in combination with the high group velocity\nachieved through the metasurface design, enable long-range propagation,\nexceeding hundreds of micrometers even with an 80% excitonic component.\nFurthermore, the design of the metasurface introduces an original\nmechanism for unidirectional propagation through polarization control,\nsuggesting a new avenue for the development of advanced polaritonic\ndevices.