Fermi-edge singularity of two dimensional electrons in asymmetric coupled double quantum wells

We present photoluminescence (PL) and PL excitation investigations on modulation doped GaAsAlGaAs asymmetric coupled double quantum wells. A Fermi-edge singularity is observed in the emissions between the electrons in the second sub-band and the holes bound at acceptors and in the valence band. The emission related to the holes bound at acceptors in the PL spectra is enhanced remarkably with decreasing excitation power for the sample occupied in the second electron sub-band, whereas this enhancement is much smaller for that which is unoccupied. These behaviours are interpreted as a consequence of the Fermi-edge singularity caused by the localisation of the holes for the former sample and the presence of an adjacent unoccupied sub-band for the latter.