Charge Separation of Dense 2D Electron-Hole Gases: Cold Exciton Ring Pattern Formation

We report on new experiment and theory that unambiguously resolve the recent puzzling observation of large diameter exciton emission halos around a laser excitation spot in two dimensional systems. We find a novel separation of plasmas of opposite charge with emission from the sharp circular boundary between these two regions. 

This charge separation allows for cooling of initially hot optically generated carriers as they dwell in the charge reservoirs for very long times, thus opening up opportunities for a detailed study of dense, low temperature exciton gas quantum staistics, and in particular suggests a route for achieving the long-sought Bose-condensation of excitons.