Highly excited exciton-polariton condensates

Abstract

Exciton polaritons are a coherent electron-hole-photon (e-h-p) system where condensation has been observed in semiconductor microcavities. In contrast to equilibrium Bose-Einstein condensation (BECs) for long lifetime systems, polariton condensates have a dynamical nonequilibrium feature owing to the similar physical structure that they have to semiconductor lasers. One of the distinguishing features of a condensate to a laser is the presence of strong coupling between the matter and photon fields. Irrespective of its equilibrium or nonequilibrium nature, exciton polaritons have been observed to maintain strong coupling. We show that by investigating the high-density regime of exciton-polariton condensates, the negative branch is directly observed in photoluminescence. This is evidence that the present e-h-p system is still in the strong-coupling regime, contrary to past results where the system reduced to standard lasing at high density.