Coulomb memory effects in the ultrafast dynamics of quantum well magnetoexcitons

Summary form only given. We study theoretically the role of exciton-exciton correlations in the ultrafast nonlinear optical response of quantum well (QW) excitons in a perpendicular magnetic field B. The important effect of the magnetic field is that, by freezing the kinetic energy of the photoexcited carriers in two spatial dimensions, it increases the relative strength of the interactions. In bulk semiconductors, experiments show a strong enhancement of the four-wave-mixing (FWM) signal with increasing field accompanied by a long nonMarkovian decay for negative time delays. We focus here on the four-particle correlations in coherent dynamics of QW excitons confined to the lowest Landau level (LL).