Optical Traps for Dark Excitons

We propose a mechanism for optical trapping of dark excitons by linearly polarized unabsorbed standing waves, with a potential depth of the order of a few meV. Since this trapping, based on carrier exchanges with virtual excitons coupled to unabsorbed photons, equally acts on bright and dark states, Bose-Einstein condensation of excitons-which occurs in dark states-must appear as dark spots in a cloud of bright excitons, at the trap potential minima, when the temperature decreases.