Optically resolved spin dynamics in semiconductor quantum structures

In this talk, we present our recent progress of spin diffusion dynamics in n-GaAs and a two-dimensional electron gas (2DEG) of high mobility investigated by means of time- and spatially resolved magneto-optic Kerr rotation. In n-GaAs we have observed spin diffusions of a sublinear type, which points to a spin diffusivity of exponentially decaying to a constant value. By performing Kerr spectral scanning at different bath temperature, we can determine the dynamical electron temperature by using the characteristic linewidth of a transient Kerr spectrum.We conclude that hot carriers can remarkably make spin diffusions faster for a nondegenerate electron gas. In contrast for a degenerate 2DEG, we have detected faster spin diffusions of a superliner type, which means a spin diffusivity of exponentially growing to a constant value. This is a remarkable consequence of spin Coulomb drag (SCD) effect. The spin diffusions can be well reproduced by using the dynamical SCD effect, and it is found that optical holes can efficiently affect spin diffusions if the spin-drag transresitivity is comparable with the charge resistivity. In the end, I will shortly introduce spin noise spectroscopy which has been recently established in my lab.