External-field-dependent enhancement of internal Coulomb interactions in time-resolved four-wave mixing

Summary form only given. Time-resolved four-wave mixing (TRFWM) has been extensively used to study the influence of Coulomb interactions on the free induction decay of excitons in semiconductor quantum-well systems. We show that the ratio between the Coulomb-mediated and the pure phase space occupation signal can be changed by more than an order of magnitude by changing the external field. The experiments are performed on a high-quality GaAs-AlGaAs superlattice of 35 periods of 97-AA wells and 17-AA barriers.