Loss of coherence in cavity-polariton condensates: effect of disorder vs. exciton reservoir

Time evolution of long-range spatial coherence in a freely decaying cavity-polariton condensate excited resonantly in a high-Q GaAs microcavity (MC) 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 blueshift α|ψ²| gets comparable to the characteristic amplitude of the disorder potential δE_LP . The disorder is found to reveal itself at α|ψ²| ≤ δE_LP 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.