The Role of Spin-Flip Collisions in a Dark-Exciton Condensate

Subhradeep Misra, Michael Stern, Vladimir Umansky, Israel Bar-Joseph

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We show that a Bose-Einstein condensate consisting of dark excitons forms in GaAs coupled quantum wells at low temperatures. We find that the condensate extends over hundreds of micrometers, well beyond the optical excitation region, and is limited only by the boundaries of the mesa. We show that the condensate density is determined by spinflipping collisions among the excitons, which convert dark excitons into bright ones. The suppression of this process at low temperature yields a density buildup, manifested as a temperature-dependent blueshift of the exciton emission line. Measurements under an in-plane magnetic field allow us to preferentially modify the bright exciton density and determine their role in the system dynamics.We find that their interaction with the condensate leads to its depletion.We present a simple rate-equations model, which well reproduces the observed temperature, power, and magnetic-field dependence of the exciton density.

Original languageEnglish
Article numbere2203531119
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number32
StatePublished - 9 Aug 2022

Bibliographical note

Publisher Copyright:
© 2022 the Author(s).


  • Bose-Einstein condensation
  • GaAs
  • excitons
  • optical spectroscopy
  • quantum wells


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