Steady state oscillations of circular currents in concentric polariton condensates.

Concentric ring exciton polariton condensates emerging under non-resonant laser pump in an annular trapping potential support persistent circular currents of polaritons. The trapping potential is formed by a cylindrical micropillar etched in a semiconductor microcavity with embedded quantum wells and a repulsive cloud of optically excited excitons under the pump spot. The symmetry of the potential is subject to external control via manipulation by its pump-induced component. In the manuscript, we demonstrate excitation of concentric ring polariton current states with predetermined vorticity which we trace using interferometry measurements with a spherical reference wave. We also observe the polariton condensate dynamically changing its vorticity during observation, which results in pairs of fork-like dislocations on the time-averaged interferogram coexisting with azimuthally homogeneous photoluminescence distribution in the micropillar.

Lasing in Bose-Fermi mixtures.

Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also been developed based on Bose-Einstein condensates of exciton-polaritons in semiconductor microcavities. These electrically neutral bosons coexist with charged electrons and holes. In the presence of magnetic fields, the charged particles are bound to their cyclotron orbits, while the neutral exciton-polaritons move freely. We demonstrate how magnetic fields affect dramatically the phase diagram of mixed Bose-Fermi systems, switching between fermionic lasing, incoherent emission and bosonic lasing regimes in planar and pillar microcavities with optical and electrical pumping. We collected and analyzed the data taken on pillar and planar microcavity structures at continuous wave and pulsed optical excitation as well as injecting electrons and holes electronically. Our results evidence the transition from a Bose gas to a Fermi liquid mediated by magnetic fields and light-matter coupling.