Spin-dependent electron many-body effects in GaAs

Abstract

Time- and polarization-resolved differential transmission measurements employing same and oppositely circularly polarized $150\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ optical pulses are used to investigate spin characteristics of conduction band electrons in bulk GaAs at $295\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Electrons and holes with densities in the $2\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}--{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ range are generated and probed with pulses whose center wavelength is between 865 and $775\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. 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 $865\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, 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 $775\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ 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 $130\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$.