Mathieu Alloing, Mussie Beian, David Fuster, Yolanda Gonzalez, Luisa Gonzalez, Roland Combescot, Monique Combescot, Francois Dubin
Bose-Einstein condensation in dilute systems is a fascinating quantum phenomenon and its experimental observation in ultracold atomic vapors a milestone. Here, we report on experimental evidence for its occurrence in a gas of semiconductor excitons. The internal degrees of freedom of these subtle bosons plays a major role in their condensation. Indeed, excitons exist in two bright and two dark states. Dark excitons having the lowest energy, the Bose-Einstein condensate of excitons is a priori dark, i.e. not coupled to light. However, above a density threshold, carrier exchanges between bright and dark excitons bring a bright component to the condensate which becomes "gray" and can be studied through its bright part. Below a few Kelvin, our experiments display the very weak emission of spatially coherent and linearly polarized light expected for such a "gray" condensate which hides a large exciton density in its dark component.
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http://arxiv.org/abs/1304.4101
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