Spin Orientation of Excitons in Asymmetric Semiconductor Nanostructures

We performed optical orientation experiments for excitons in a biased asymmetric GaAs-Ga(Al)As double quantum well structure. We excited quasi-resonathly (with circularly polarized light) the ground wide well exciton transition and recorded the evolution in time of the polarization of the resulting luminescence line. We show that the measured initial polarization and depolarization time sensibly vary with the applied field around the flat-band regime. We examine theoretically the role of the intra-well (induced by the field) and inter-well (tunnel) couplings on the relaxation of the wide well exciton spin.