Spin Dynamics in Semiconductors
The electron-spin dynamics may be tested taking advantage of the particular structure of electron states, which posses a well-defined total angular momentum or “pseudo-spin”. The selection rules of the optical transitions allow to inject carriers with a controlled spin into the samples and to follow their relaxation by using polarized light beams. The study of the spin evolution of charged carriers in semiconductors is motivated by the possibility to associate (in the same device) the electron spin for stocking of information and its charge for transportation of this information. The spin evolution of the charged carriers in a semiconductor is not only determined by the life time of a spin state but also by the coherent superposition of the different spin states and the time during which such a superposition may be maintained. We measure the coherence time and the lifetime of spin states of electrons, holes, or of excitons in semiconductor nanostructures, such as quantum wells or quantum points of different compounds (GaAs, CdTe, CuCl, GaN) . We develop for these studies experimental techniques of femtosecond spectroscopy as pump-probe and four-wave mixing, which are specific for the determination of the spin evolution.