Long-lived spatially indirect excitons in coupled GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells

We present nanosecond time-resolved measurements of the low-temperature photoluminescence in coupled GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells. Working with 10.0-nm and 15.0-nm GaAs quantum wells coupled through a 3.0-nm ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As barrier layer, we observe spatially indirect excitons with lifetimes in excess of 200 nsec—an enhancement of more than 2 orders of magnitude over the lifetime of the spatially direct exciton. As a result, extremely cold GaAs exciton gases become possible, a prerequisite for testing recent predictions of quantum-statistical behavior in this system.