title: Particle correlations and evidence for dark state condensation in a cold dipolar exciton fluid.
abstract: Dipolar excitons are long-lived quasi-particle excitations in semiconductor heterostructure that carry an electric dipole. Cold dipolar excitons are expected to have new quantum and classical multi-particle correlation regimes, as well as several collective phases, resulting from the intricate interplay between the many-body interactions and their quantum nature. Here we show experimental evidence of a few correlation regimes of a cold dipolar exciton fluid, created optically in a semiconductor bilayer heterostructure. In the higher temperature regime, the average interaction energy between the particles shows a surprising temperature dependence, which is evidence for correlations beyond the mean field model. At a lower temperature, there is a sharp increase in the interaction energy of optically active excitons, accompanied by a strong reduction in their apparent population. This is evidence for a sharp macroscopic transition to a dark state, as has been suggested theoretically.
authors: Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors: Yehiel
authors: Y
authors: Shilo
authors: Kobi
authors: K
authors: Cohen
authors: Boris
authors: B
authors: Laikhtman
authors: Ken
authors: K
authors: West
authors: Loren
authors: L
authors: Pfeiffer
authors: Ronen
authors: R
authors: Rapaport