Breakdown of the one-electron picture in optical spectroscopy of low-dimensional electron systems: three anomalies around the Fermi level

We report three distinct anomalies in emission, absorption and linear emission polarization of two-dimensional degenerate electron systems with tunable lateral potential modulation. We show that they occur for convergent as well as singular Fermi edges with a unique threshold energy below the Fermi level. The resulting spectral hole for convergent edges significantly breaks down the determination of the Fermi energy in the one-electron picture from photoluminescence spectra.