Spatially indirect excitons in a coupled quantum well structure were studied by means of polarization and time resolved photoluminescence. A strong degree of circular polarization (> 50%) in emission was achieved when the excitation energy was tuned into resonance with the direct exciton state. The indirect transition remained polarized several tens of nanoseconds after the pumping laser pulse, demonstrating directly a very long relaxation time of exciton spin. The observed spin memory effect exceeds the radiative lifetime of the indirect excitons.
@article{arxiv.1004.0082,
title = {Long exciton spin memory in coupled quantum wells},
author = {Katarzyna Kowalik-Seidl and Xaver P. Vögele and Bernhard N. Rimpfl and Stephan Manus and Dieter Schuh and Werner Wegscheider and Alexander W. Holleitner and Jörg P. Kotthaus},
journal= {arXiv preprint arXiv:1004.0082},
year = {2015}
}