Coherent spin dynamics of an interwell excitons gas in GaAs/AlGaAs   coupled quantum wells
  The spin dynamics of an interwell excitons gas has been investigated in n-i-n GaAs/AlGaAs coupled quantum wells (CQWs). In these heterostructures the electron and the hole are spatially separated in neighboring quantum wells by a narrow AlAs barrier, when an electric field is applied. The time evolution kinetics of the interwell exciton photoluminescence has been measured under resonant excitation of the 1sHH intrawell exciton, using a pulsed tunable laser. The formation of a collective exciton phase in time and the temperature dependence of its spin relaxation rate have been studied. The spin relaxation rate of the interwell excitons is strongly reduced in the collective phase. This observation provides evidence for the coherence of the indirect excitons collective phase at temperatures below a critical $T_c$. 
A.V. Larionov, V.E. Bisti, M. Bayer, J. Hvam, and K. Soerensen