Coherent spin dynamics of an interwell excitonic gas in Ga As ∕ Al Ga As coupled quantum wells

The spin dynamics of an interwell exciton gas has been investigated in $n\text{\ensuremath{-}}i\text{\ensuremath{-}}n$ $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ coupled quantum wells. The time evolution kinetics of the interwell exciton photoluminescence has been measured under resonant excitation of the $1s$ heavy-hole 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 interwell exciton collective phase at temperatures below a critical ${T}_{c}$. A theoretical analysis of the interwell exciton spin-flip dynamics has been developed.