INHIBITION OF EXCITON SPIN RELAXATION BY LONGITUDINAL-OPTICAL PHONON EMISSION

We study the interplay between a fast energy relaxation process and th e spin depolarization for excitons in undoped double quantum wells. We show that the exciton depolarization is significantly inhibited when a fast channel exists for the energy relaxation after a nonresonant ex citation. Specifically, we consider the favorable case of a strongly c oupled asymmetric double quantum well where the first heavy and light exciton levels of the thin well are separated by a longitudinal-optica l phonon energy. The relevance of different relaxation mechanisms is a lso discussed.