Spin relaxation in low-dimensional systems

We review some of the newest findings on the spin dynamics of carriers and excitons in GaAs/GaAlAs quantum wells. For intrinsic wells, whose optical p roperties are dominated by excitonic effects,, we show that exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors. For doped wells, the two spin components of an optically cr eated two-dimensional electron gas are well described by Fermi-Dirac distri butions with a common temperature but different chemical potentials. The ra te of the spin depolarization of the electron gas is found to be independen t of the mean electron kinetic energy but accelerated by thermal spreading of the carriers.