Femtosecond circular dichroism study of nonthermal carrier distributions in two- and zero-dimensional semiconductors

We report the time-resolved circular dichroism induced by nonthermal distributions of carriers in GaAs quantum wells, separating completely, for the first time, the effects of screening and phase space filling. Thermalization of the initial excitation is strongly inhibited when carriers are laterally confined into zero dimensions by a large perpendicular magnetic field.