Different Phases of Polariton Lasers

Nonequilibrium systems can exhibit new types of phase transitions not found in equilibrium ones, such as spontaneous pattern formation [1], [2] and phase separation. An interesting platform for studying such phenomena is the exciton-polaritons in semiconductor microcavities [3]. As half-light half-matter quasi-particles, polaritons form an open, nonlinear system, where the non-equilibrium counterpart of a rich variety of many-body phases have been established, such as dynamic Bose-Einstein condensate (BEC), Berezinskii-Kosterlitz-Thouless (BKT) like phase in a two-dimensional cavity, and a Bardeen Cooper Schrieffer (BCS) like polariton laser. The interplay between pumping, thermalization, decay and strong polariton interactions may also give rise to phenomena unique to non-equilibrium systems, such as solitons and spontaneous limit cycle oscillations. Here we focus on the hitherto obscured phase separation in a steady-state non-equilibrium polariton condensate.