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 $n=1\mathrm{hh}$ exciton bleaching. In addition, we find that the strength of long-range Coulomb screening on the $n=1\mathrm{hh}$ exciton bleaching is only two to three times weaker than that of the phase-space filling at $10\mathrm{K}$.

Figure 1

Linear absorption spectrum of $GaAs∕AlGaAs$ MQW structure at $10\mathrm{K}$, including the spectral shapes of the pump and probe pulses.

Figure 2

Low temperature differential transmission spectra measured at both $n=1\mathrm{hh}$ and $n=2\mathrm{hh}$ excitons. The inset shows the enlarged view of differential transmission spectra near the $n=2\mathrm{hh}$ excitons.

Figure 3

The fractional change of exciton binding energy as a function of relative decrease of exciton oscillator strength.

Figure 4

Relative strength of PSF and CS on the $n=1\mathrm{hh}$ exciton bleaching for various excitation densities. The dashed line corresponds to the theoretical calculation.