Coulomb memory effects and higher-order Coulomb correlations in the excitonic optical stark effect

Differential absorption spectra of high quality InGaAs quantum wells were measured by means of pump-probe spectroscopy as a function of pump-probe delay, for different polarizations of the pulses, and different spectral detunings of the pump beam with respect to the Is heavy-hole exciton. A clear redshift of the heavy-hole resonance is observed for large detunings and opposite circularly polarized pulses. Microscopic calculations that include not only the Hartree-Fock contribution but also higher-order Coulomb correlations reproduce the experimental findings very well. It is shown that the redshift is caused by Coulomb memory effects and is further enhanced due to the presence of the bound biexciton.