Evidence for dipole-dipole hopping of GaAs quantum well excitons

We present measurements of the energy relaxation of quasi-two-dimensional excitons in the hopping regime. Under a variety of experimental conditions, the mean energy decays in proportion to In t. We interpret this result naturally in a model based on the dipole-dipole mechanism for energy loss hops. The model achieves semiquantitative agreement with the observed energy loss rates.