Loss of coherence in cavity-polariton condensates: Effect of disorder versus exciton reservoir

Time evolution of long-range spatial coherence in a freely decaying cavity-polariton condensate excited resonantly in a high-Q GaAs microcavity is found to be qualitatively different from that in nonresonantly excited condensates. The first-order spatial correlation function g(1)(r1,r2) in response to resonant 1.5 ps pump pulses at normal incidence leaving the exciton reservoir empty is found to be nearly independent of the excitation density. g(1) exceeds 0.7 within the excited spot and decreases very slowly in the decaying and expanding condensate. It remains above 0.5 until the polariton blue shift α|ψ2| gets comparable to the characteristic amplitude of the disorder potential δELP. The disorder is found to reveal itself at α|ψ2|≲δELP in fast and short-range phase fluctuations as well as vortex formation. They lead to oscillations in g(1)(t), but have little effect on the overall coherence, which is well reproduced in the framework of the Gross-Pitaevskii equations.