Optical signatures of energy-level statistics in a disordered quantum system

Time-resolved measurements of the resonant Rayleigh scattering from quantum well excitons are shown to provide information on the energy-level statist ics of the localized exciton states. The signal transients are reproduced b y a microscopic quantum model of the exciton two-dimensional motion in pres ence of spatially correlated disorder. This model allows quantitative deter mination of the average energy separation between the localized states. Her e this quantity turns out to be only a few times smaller than the average d isorder amplitude, proving that spatial correlation and quantum mechanics a re equally important in the description of the exciton localization process .