Ghost Branch Photoluminescence From a Polariton Fluid Under Nonresonant Excitation

An expanding polariton condensate is investigated under pulsed nonresonant excitation with a small laser pump spot. Far above the condensation threshold we observe a pronounced increase in the dispersion curvature with a subsequent linearization of the spectrum and strong luminescence from a ghost branch orthogonally polarized with respect to the linearly polarized condensate emission. The presence of the ghost branch has been confirmed in time-resolved measurements. The dissipative and nonequilibrium effects in the photoluminescence of polariton condensates and their excitations are discussed.