Dynamics of optically injected two-dimensional currents

We investigate the charge and spin dynamics of optically injected currents in multiple quantum well structures using a hydrodynamic model. The dynamics is very complex even on time scales of the order of 1 ps due to the interplay of Coulomb forces, electron-hole drag effects, and nonlinearity of the equations of motion. Our analysis is based on a numerical approach employing an expansion of the calculated quantities in a Hermite-Gaussian basis. We calculate the evolution of the density of injected carriers, analyze the pattern of charges after the injection, and extract the parameters that characterize the overall charge displacement in the optical pump-probe and terahertz radiation experiments. While these two parameters would take on the same value if the injected charge distributions moved rigidly, we find that their observed values should be different due to the complex behavior of the carrier motion. The spin flows arising from the spin-dependent skew scattering of electron by holes and corresponding spin density distributions are calculated and analyzed.