Nonlinear Photoluminescence Kinetics of Indirect Excitons in Coupled Quantum Wells

Abstract

We report the strongly nonlinear dependence of indirect exciton photoluminescence (PL) kinetics on excitation density. In the indirect regime characterized by a slow exciton recombination, at high excitation densities, low magnetic fields, low temperatures, and for samples with small in-plane disorder, we observe that the indirect exciton PL intensity increases sharply within a few nanoseconds after the excitation is switched off. This PL intensity jump is also accompanied by a subsequent PL decay rate that increases with excitation density. The effects are observed only when the estimated occupancies of the lowest energy exciton states exceed unity. The system of indirect (interwell) excitons in coupled quantum wells (CQWs) is characterized by much longer indirect exciton recombination time compared to single-layer exciton systems. Therefore, CQWs provide a unique opportunity for studying low temperature 2D exciton systems. In particular, the long lifetime of indirect excitons pro