Dephasing of Quasi-2D Biexcitons

The temperature dependent dephasing of the biexcitonic resonance in a homogeneously broadened single quantum well is studied by transient four-wave mixing. Using cross-linear excitation polarization, we deduce the biexcitonic and excitonic dephasing rates from the delay-time dependence of the FWM signal at the biexcitonic resonance for negative and positive delay times, respectively. The ratio between the dephasing rates of biexcitons and excitons is found to be close to two for kBT larger than the biexciton binding energy. At lower temperatures, the ratio drops significantly. This demonstrates that biexcitonic dephasing at high temperature is connected to thermal dissociation, and that the intrinsic low-temperature dephasing time of biexcitons can be longer than that of excitons.