Optical anomalies of the two-dimensional electron gas in the extreme magnetic quantum limit.

Bandgap optical recombination from the two-dimensional electron gas in GaAS-(AlGa)As quantum wells was measured in the regime of the fractional quantum Hall effect. New intrinsic emission lines emerge at Landau level filling factors vu ~ 1 and vu 0.8. We propose that these anomalies are due to changes in the screening response of the Fermi sea to the Coulomb potential of the hole when vu = 1. The anomaly at vu ~ 1 is governed by the Zeeman splitting of the lowest Landau level and the one at vu 0.8 by excitations related to the fractional quantum Hall state at vu = 2/3.