Spin-dependent electron many-body effects in GaAs

Time- and polarization-resolved differential transmission measurements employing same and oppositely circularly polarized 150 fs optical pulses are used to investigate spin characteristics of conduction band electrons in bulk GaAs at 295 K. Electrons and holes with densities in the 2x10(16) cm(-3)-10(18) cm(-3) range are generated and probed with pulses whose center wavelength is between 865 and 775 nm. The transmissivity results can be explained in terms of the spin sensitivity of both phase-space filling and many-body effects (band-gap renormalization and screening of the Coulomb enhancement factor). For excitation and probing at 865 nm, just above the band-gap edge, the transmissivity changes mainly reflect spin-dependent phase-space filling which is dominated by the electron Fermi factors. However, for 775 nm probing, the influence of many-body effects on the induced transmission change are comparable with those from reduced phase space filling, exposing the spin dependence of the many-body effects. If one does not take account of these spin-dependent effects one can misinterpret both the magnitude and time evolution of the electron spin polarization. For suitable measurements we find that the electron spin relaxation time is 130 ps.