Dynamics of spatial coherence and momentum distribution of polaritons in   a semiconductor microcavity under conditions of Bose-Einstein condensation
  The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation are investigated in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses. It is shown that the onset of the condensate first order sparial coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct measurements and that calculated from the coherence spatial distribution. This discrepancy is observed at the fast initial stage of the polariton system kinetics and, apparently, results from the strong spatial nonuniformity of the phase of the condensate wave function, which equilibrates on a much longer time scale. 
D. A. Mylnikov, V. V. Belykh, N. N. Sibeldin, V. D. Kulakovskii, C.   Schneider, S. H\"ofling, M. Kamp, A. Forchel
cond-mat.quant-gas cond-mat.mes-hall quant-ph