1. Spin diffusion, precession, and drift.
In the experiments, the electronic spin is injected optically by circularly polarized light in a micron-size region and its diffusion in the presence of electric and magnetic field is then measured optically by the Faraday rotation. The measurements are well described by theory based on the diffusion equation for the spin density matrix as a function of position.
2. Spin noise.
Spin noise in a probed region of the sample is modified by motion of the spin-carrying particles in and out of that region. I studied this effect for non-interacting fermions in different regimes of temperature (degenerate vs. nondegenerate case) and disorder (ballistic vs. diffusive motion). In all these regimes, I calculated the noise power spectrum starting from the spin response function averaged over the probed region and using the fluctuation-dissipation theorem, thus obtaining the magnitude of the noise signal and its characteristic frequency. My theoretical results are being used to interpret Faraday rotation measurements of electron spin noise in Rb vapor and conduction electrons in GaAs. Rb vapor corresponds to the nondegenerate ballistic case and conduction electrons in GaAs corresponds to the degenerate case with ballistic or diffusive transport depending on the experimental parameters. For the physical parameters of these systems, I will discuss the sensitivity of the measuring devices that the theory requires to observe the spin noise.