Non‐Equilibrium Bose–Einstein Condensation of Exciton‐Polaritons in Silicon Metasurfaces

Exciton‐polaritons (EPs) are hybrid light–matter quasi‐particles with bosonic character formed by the strong coupling between excitons in matter and photons in optical cavities. Their hybrid character offers promising prospects for the realization of non‐equilibrium Bose–Einstein condensates (BECs), and room‐temperature BECs are possible with organic materials. However, the thresholds required to create BECs of organic EPs remain still high to allow condensation with electrical injection of carriers. One of the factors behind these high thresholds is the very short cavity lifetimes, leading to a fast EP decay and the need to inject higher exciton densities in the reservoir to form the condensate. Here a BEC of EPs in organic dyes and all‐dielectric metasurfaces at room temperature is demonstrated. By using dielectric metasurfaces that exhibit very low losses it is possible to achieve cavity lifetimes long enough to allow an efficient population of EP states via vibrational relaxation and radiative pumping. It is shown how polariton lasing or non‐equilibrium Bose–Einstein condensation is achieved in several cavities, and one of the lowest reported thresholds for BECs in organic materials is observed. The first demonstration of a room‐temperature polariton condensate on an all‐dielectric metasurface is presented. Thanks to the engineered low radiative losses of the silicon metasurface, and the efficient relaxation of the dye, a condensate is observed at the low threshold of Pth = 8.2 µJ cm−2. The presence of radiative pumping allows to tune the condensation energy with the period.