Precursors of the excitonic insulator in excited quantum wells

The theory of the magnetooptical properties of highly excited quantum wells is reviewed with emphasis on recent experimental work in a collaboration led by the Chernogolovka group. Realistic numerical calculations strongly support the interpretation of the experimental magnetoluminescence spectra in terms of bound electron-hole pairs, but at the experimental plasma temperatures of 40-50 K phase coherence and thus observation of the excitonic insulator state is not yet achieved. Important screening effects beyond the Hartree-Fock approximation exist even at magnetic fields of 10 T. At lower densities, evidence of dynamical screening of the electron-hole interaction is found.