Polaron-Polariton Bose-Einstein Condensation Lasing via Longitudinal Optical Phonon Scattering in GaN-Based...

Exciton-polaritons, hybrid states composed of excitons and photons under strong coupling, play a crucial role in investigating Bose-Einstein condensation (BEC) and optoelectronics. However, the relaxation bottleneck in exciton-polaritons, arising from reduced scattering efficiency with acoustic phonons, hinders the achievement of thermal equilibrium Bose-Einstein condensation (BEC). Here, by invoking the polaronic effect of the exciton, we present the first observation of polaron-polariton BEC in a GaN-based microcavity. The dispersion pattern in k-space reveals a typical middle polariton (MP) branch of polaron-polaritons. This unique dispersion structure enables a novel relaxation route through LO-phonon-mediated scattering for polaron-polaritons, overcoming the phonon bottleneck observed in exciton-polaritons. By utilizing this mechanism, we achieve a robust polaron-polariton BEC, which is confirmed by the characteristics of massive occupation of the ground state, linear polarization buildup, and long-range spatial coherence. Our findings provide new insights into thermal equilibrium BEC and high-performance polariton quantum devices with GaN materials.