Electron-Hole Correlation Singularities in the Absorption Spectra of Modulation Doped GaAs-AlGaAs Quantum Wells.

By measuring the temperature dependence of the optical absorption and luminescence of modulation-doped GaAsAlGaAs quantum wells, we show that the lowest energy absorption peak is dramatically different in character from the excitonic peaks of undoped wells, changing strongly between 10 and 80K. Instead, we find good qualitative agreement with calculations based on the recently predicted many-body "correlation singularity" [Schmitt-Rink et al., Phys. Rev. B33,1183(1986)]. In this model, the absorption peak is caused by screening, which correlates the hole with the sea of electrons, thereby enhancing the absorption.