Room-temperature superfluidity of organic polaritons

Exciton-polaritons are hybrid light-matter particles that can be created in semiconductor microcavities. These quasiparticles can possess enhanced third-order nonlinearities as compared to bare photons due to the resonant behaviour and the matter component. In this work, we will demonstrate the superfluid flow of polaritons at room-temperature in an organic microcavity. These observations are a result of the strong polariton-polariton nonlinearities present in such structures. Polaritons can be selectively created with a fixed flow velocity and observed to flow in the sample plane. When the density of a polariton condensate is increased, its excitation spectrum acquires a linear shape around the pump wavevector, which is related to the sound velocity for elementary excitations. When this sound velocity increases beyond the flow velocity, scattering becomes disallowed in agreement with the Landau criterion for superfluidity. This transition is observed for flow across defects in the sample both in real space and in phase space as a function of the polariton density. The prospect of creating devices that are immune from scattering is attractive for future room-temperature polaritonic devices.