Physica E 2 (1998) 186 — 190 Many body effects on the spin relaxation of electrons in GaAs quantum wells M.D. Martı´n, E. Pe´rez, L. Vin  a*, L. Gravier, M. Potemski, K. Ploog, A. Fisher  Departamento de Fisica Materiales, C-IV Universidad Autonoma, E-28049 Madrid, Spain  GHMFL, MPI/FKF & CNRS, F-38042 Grenoble, France  PDI fu ( r Festko ( rperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin, Germany  MPI fu ( r Festko ( rperforshung, D-8000 Stuttgart, Germany Abstract The dynamics and energy spectrum of spin-polarized electron gases are studied using time- and polarization-resolved interband luminescence experiments in p-type, modulation-doped quantum wells. A non-linear dependence of the electron spin relaxation versus excitation intensity is observed and attributed to a strong coupling of single electronic spin relaxation to the decay of the total polarization of the hole gas. The evolution of the luminescence spectra versus time and excitation power shows non-equilibrium distributions of the two components of the spin-unbalanced electron gas with similar temperatures but different Fermi energies. The spin-dependent band filling dominates over renormaliz- ation effects and leads to an appreciable shift between the emission spectra with different helicities of circular polarization.  1998 Elsevier Science B.V. All rights reserved. Keywords: Spin dynamics; High density-effects; Time-resolved spectroscopy A circularly polarized, near-band edge, excita- tion of a semiconductor structure permits the creation of a gas of photoexcited electrons with appreciable different populations of spin-up and spin-down components [1]. The dynamics and en- ergy spectrum of this spin-unbalanced electron gas can be conveniently investigated in p-type struc- tures by measuring the circularly polarized recom- bination between photocreated electrons and the non-polarized gas of holes, which mostly originates * Corresponding author. Fax: #34 1 397 8579; e-mail: luis.vina@uam.es. from doping. A variety of optical pumping experi- ments, including time-resolved spectroscopy, have been employed to determine the mechanisms of spin relaxation and its dependence on doping, tem- perature, dimensionality, etc. [2]. Only recent stud- ies on excitons raised the problem of interactions within a gas of spin polarized carriers [3]. In this paper, the time evolution of the two spin components of a photocreated electron gas is inves- tigated as a function of the density of carriers excit- ed with a picosecond laser pulse. Exciting a p-type GaAs quantum well below the light-hole reson- ance, electrons with almost purely one spin com- ponent are photocreated. Filling of the conduction 1386-9477/98/$19.00  1998 Elsevier Science B.V. All rights reserved PII: S 1 3 8 6 - 9 4 7 7 ( 9 8 ) 0 0 0 4 0 - X