Relative strength of the screened Coulomb interaction and phase-space filling on exciton bleaching in multiple quantum well structures

We investigate the effect of resonantly excited excitons on the bleaching of $n=1$ and $n=2$ heavy-hole (hh) exciton resonances in $GaAs$ multiple-quantum-well structures by using a pump-probe spectroscopic technique at low temperature under quasi-stationary excitation conditions. In particular, we present direct observation of long-range Coulomb screening by two-dimensional exciton-exciton interactions along with the unambiguous discrimination of screened Coulomb interaction and phase-space filling on the $n=1\phantom{\rule{0.3em}{0ex}}\mathrm{hh}$ exciton bleaching. In addition, we find that the strength of long-range Coulomb screening on the $n=1\phantom{\rule{0.3em}{0ex}}\mathrm{hh}$ exciton bleaching is only two to three times weaker than that of the phase-space filling at $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.