Spontaneous coherence of indirect excitons in a trap
  We report on the emergence of spontaneous coherence in a gas of indirect excitons in an electrostatic trap. At low temperatures, the exciton coherence length becomes much larger than the thermal de Broglie wavelength and reaches the size of the exciton cloud in the trap. 
Alexander A. High, Jason R. Leonard, Mikas Remeika, Leonid V. Butov,   Micah Hanson, and Arthur C. Gossard
cond-mat.quant-gas