THE EXCITON-EXCITON CONTINUUM AND ITS CONTRIBUTION TO 4-WAVE-MIXING SIGNALS

The combined influence of biexcitons and tile two-exciton scattering c ontinuum is analyzed. The analysis is based on a density matrix descri ption of a two-band semiconductor accounting for mean-field contributi ons, bound biexcitons and the correlated parts of the two-exciton scat tering continuum on a common footing. Consistent with the microscopic formulation, the influence of biexcitons as well as that of the two-ex citon continuum is represented by a correlation kernel which is obtain ed from an integral equation. For a one-dimensional model four-wave mi xing signals are calculated solving numerically the resulting coupled nonlinear equations for excitation conditions in the vicinity oi tile Is resonance. A strong compensation between the exciton-exciton contin uum and the mean-field contribution is found for all excitation condit ions studied. Surprisingly, biexcitonic signatures turn out to be enha nced when continua are included in the description.