Abstract
We study spatially trapped ensembles of dipolar excitons in coupled quantum wells by means of photoluminescence and photocurrent spectroscopy. The photogenerated excitons are confined in very clean GaAs double quantum well structures and electrostatically trapped by local gate electrodes. We find that the common approach of electrostatic trap geometries can give rise to an in-plane imbalance of charge carriers especially when an over-barrier excitation is utilized. The excess charge carriers can give rise to an effective parabolic confinement potential for the excitons. In photoluminescence spectra, we identify the emission of both neutral indirect excitons and states influenced by the excess charge carrier density. We find that the charge imbalance in the excitonic ensemble strongly influences the radiative lifetimes of both. Our findings shine a new light on the properties of trapped dipolar exciton ensembles. This is of significant relevance to common interpretations of experimental results in terms of signatures for the formation of ‘dark’ and ‘gray’ excitonic condensates.
Highlights
The research on fundamental many-body interactions and correlations in cold bosonic ensembles is an ongoing and very active field with stimulating experiments on ultra-cold atom gases [1,2,3,4,5] as well as on solid state exciton [6,7,8,9,10] and exciton-polariton ensembles [11, 12]
Even though promising experimental results are reported [18,19,20], an unambiguous proof for an excitonic Bose–Einstein condensate (BEC) is still missing and motivates detailed experimental investigation of parameters influencing the interactions in exciton ensembles [21, 22]
The corresponding exciton complexes have been attributed to so-called trion states with a neutral exciton being bound to a free charge carrier [24, 35,36,37,38,39,40,41,42,43,44,45,46,47,48,49], albeit recent theory and experiments point out an alternative explanation in terms of attractive and repulsive exciton-polaron branches of excitons being dressed with the interaction with excess charge carriers [50, 51]
Summary
47907, United States of America 4 School of Electrical and Computer Engineering and School of Materials Engineering, Purdue University, West Lafayette, IN 47907, United States of America. Original content from this 5 Center for NanoScience and Fakultät für Physik, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, D-80539 Munich, work may be used under the terms of the Creative. Commons Attribution 3.0 6 Institute of Physics, University of Münster, 48149 Münster, Germany licence.
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