Electron spin relaxation as evidence of excitons in an electron-hole   plasma
  We exploit the influence of the Coulomb interaction between electrons and holes on the electron spin relaxation in a (110)-GaAs quantum well to unveil excitonic signatures within the many particle electron-hole system. The temperature dependent time- and polarization-resolved photoluminescence measurements span five decades of carrier density, comprise the transition from localized excitons over quasi free excitons to an electron-hole plasma, and reveal strong excitonic signatures even at relatively high densities and temperatures. 
S. Oertel, S. Kunz, D. Schuh, W. Wegscheider, J. H\"ubner, and M.   Oestreich
cond-mat.mes-hall