MAGNETICALLY ENHANCED EXCITON-EXCITON CORRELATIONS IN SEMICONDUCTORS

Recent experiments on fs time-resolved coherent wave mixing under a hi gh magnetic field have revealed a new regime at low excitation densiti es which is not in accordance with the semiconductor Bloch equations. We present a theory of coherently driven biexcitons in a strong magnet ic field, which - due to the restriction of excitonic degrees of freed om - results in a strong enhancement of Coulomb correlation effects. T he theory describes most of the observed features. Especially, the slo w rising time of the time-integrated four-wave mixing signal is shown to result from biexcitonic correlation. The same interaction effects y ield a strong dependence of the oscillator strength of the heavy- (hh) and light-hole (lh) excitons on the time delay between the two pulses . (C) 1998 Published by Elsevier Science B.V. All rights reserved.