''Gray'' BCS Condensate of Excitons and Internal Josephson Effect

Roland Combescot (1) , Monique Combescot (2)

1 LPS - Laboratoire de Physique Statistique de l'ENS
2 INSP - Institut des Nanosciences de Paris

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. Here, we show that, under a density increase, the dark exciton condensate must acquire a bright component due to carrier exchange in which dark excitons turn bright. This, however, requires a density larger than a threshold which seems to fall in the forbidden region of the phase separation between a dilute exciton gas and a dense electron-hole plasma. The BCS-like condensation which is likely to take place on the dense side, must then have a dark and a bright component-which makes it ``gray.'' It should be possible to induce an internal Josephson effect between these two coherent components, with oscillations of the photoluminescence as a strong proof of the existence for this ``gray'' BCS-like exciton condensate.

Domaines: Matière Condensée [cond-mat]

Roland Combescot, Monique Combescot. ''Gray'' BCS Condensate of Excitons and Internal Josephson Effect. Physical Review Letters, 2012, 109 (2), pp.026401. ⟨10.1103/PhysRevLett.109.026401⟩. ⟨hal-01229189⟩