Polariton-biexciton transitions in a semiconductor microcavity

The influence of four-particle correlations on the nonlinear optics of a se miconductor microcavity is determined by a pump-and-probe investigation. Ex periments are performed on a nonmonolithic microcavity which contains a ZnS e quantum well. In this system the biexciton binding energy exceeds both th e normal-mode splitting between exciton and cavity mode and all damping con stants. Oscillatory spectral features below the excitonic resonance are obs erved in the response for counterpolarized beams. Comparison with model cal culations shows that in this case the coherent nonlinearity is dominated by biexciton-exciton interactions beyond the Hartree-Fock approximation.