Collective behavior of a spin-aligned gas of interwell excitons in double quantum wells

The kinetics of a spin-aligned gas of interwell excitons in GaAs/AlGaAs double quantum wells ($n-i-n$ heterostructure) is studied. The temperature dependence of the spin relaxation time for excitons, in which a photoexcited electron and hole are spatially separated between two adjacent quantum wells, is analyzed. For this purpose, use was made of pulsed circularly polarized resonant photoexcitation of intrawell $1sHH$ excitons by a femtosecond frequency-controlled laser. A sharp increase in the spin-relaxation rate is observed for interwell excitons upon a change in temperature from 2 to 3.6 K. This effect is associated with indirect evidence of the coherence of the collective phase of interwell excitons at temperatures below the critical value.