Thermodynamics of excitons in coupled quantum wells

Because of their long lifetime in coupled quantum wells under an applied electric field, excitons may he able to reach thermodynamic quasi-equilibrium. Here we measure photoluminescencc and photoluminescence excitation spectra from a symmetric coupled double quantum well. Analysis of the spectra shows that thermodynamic quasi-equilibrium is not achieved at temperatures below 6 K, where the excitons are trapped in a metastahle distribution. At higher temperatures, quasi-equilihrium is achieved. Because of strong repulsion between the excitons, the quasi-equilihrium distribution can he modeled with a Fermi-Dirac distribution. The model quantitatively explains the striking temperature dependence of the photoluminescence lincwidth which has been previously reported.