Electrostatically trapping indirect excitons in coupled InxGa1−xAs quantum wells

Abstract

We report on photoluminescence experiments on spatially indirect excitons in an InGaAs coupled double quantum well device in which semitransparent gates are employed to tune the in-plane potential landscape. We introduce a trapping configuration in which exciton generation is spatially separated from the excitonic trapping potential. Suitably biased gates control the flow of indirect dipolar excitons from the generation area to the electrostatically defined trap. Thus the trap is filled only with indirect excitons precooled to the lattice temperature. Using a confocal microscope at liquid helium temperatures we map the in-plane distribution of excitons at various gate voltages and illumination conditions. Our small and strongly confining traps with precooled excitons demonstrate interesting many-body effects which can be interpreted in terms of the electrostatic screening, the Coulomb binding, and excitonic flows. Gate voltage dependencies of PL energy in our samples are not monotonic and can be explained by considering the nonlinear exciton flows between the elements of our structure. At strong illumination hysteretic switching of the trapped exciton population reflects a nonlinear character of the self-consistent trapping potential. An unusual nonlinear increase of the emission of the trap is likely coming from the many-body interactions in a dense exciton gas in the presence of a disorder potential at high light intensity. The designs of electrostatic traps proposed and realized here allow for stronger confinements and lower temperatures and will be used to search for coherent phenomena in dense exciton gases.