Optical control of spins in semiconductors

Recent and ongoing optical experiments on mechanisms and methods for control and gating of spin relaxation in semiconductor quantum wells are reviewed. We discuss work on high-mobility two-dimensional electron gases in (001)-grown GaAs/AlGaAs wells which reveals two new aspects of D'yakonov, Perel' and Kachorovskii (DPK) spin dynamics, namely oscillatory spin evolution in a quasi-collision-free regime at low temperatures and strong deviation from the standard expectation that spin-relaxation rate will be proportional to electron mobility at higher temperatures. The latter may indicate that electron-electron scattering, neglected hitherto, is important for spin relaxation. Experiments on (01 I)-grown GaAs/AlGaAs quantum wells confirm that this orientation leads to extension of electron spin memory by as much as two orders of magnitude at room temperature due to suppression of the major contribution to DPK spin relaxation. Results for a sample with built-in electric field give a strong indication that, for this growth orientation, room temperature spin memory may be gated by external applied voltage.