Bose-Einstein condensation and indirect excitons: a review.

We review recent progress on Bose-Einstein condensation (BEC) of semiconductor excitons. The first part deals with theory, the second part with experiments. This Review is written at a time where the problem of exciton Bose-Einstein condensation has just been revived by the understanding that the exciton condensate must be dark because the exciton ground state is not coupled to light.

Effects of fermion exchange on the polarization of exciton condensates.

Exchange interaction is responsible for the stability of elementary boson condensates with respect to momentum fragmentation. This remains true for composite bosons when single fermion exchanges are included but spin degrees of freedom are ignored. Here, we show that their inclusion can produce a spin fragmentation of the dark exciton condensate, i.

"Gray" BCS condensate of excitons and internal Josephson effect.

It has been recently suggested that the Bose-Einstein condensate formed by excitons in the dilute limit must be dark, i.e., not coupled to photons.

Bose-Einstein condensation in semiconductors: the key role of dark excitons.

Bose-Einstein condensation in semiconductors is controlled by the nonelementary-boson nature of excitons. Pauli exclusion between the fermionic components of composite excitons produces dramatic exchange couplings between bright and dark states. In microcavities, where bright excitons and photons form polaritons, they force the condensate to be linearly polarized, as observed.