Effects of electronic fourth-order correlations on the pump-probe responseof semiconductors

The pump-and-probe response of a ZnSe quantum well is investigated. In this particular sample the binding energy far exceeds both the exciton damping and the inhomogeneous broadening. A comparison between experimental data an d model calculations shows that with co-circularly polarized beams the nonl inear mean-field contributions dominate those induced by four-particle corr elations. In contrast, only the four-particle correlations contribute to th e signal in counter-circular configuration. For this configuration, the exc iton-biexciton interaction dominates the response for resonant excitation o f the exciton. The occurrence of exciton-biexciton transitions leads to a r enormalization of the period of coherent oscillations at negative pulse del ay.