Observation of a discontinuous red-shift in the emission spectrum of a two-dimensional electron gas

Photoluminescence of a high-density GaAs/AlGaAs heterostructure has been investigated up to 60 T using a quasi-continuous magnet. At a field of 27.5 T, corresponding to a filling factor of ν=2 of the 2DEG, we find that the dominant Fermi-edge-enhanced emission line disappears abruptly, and an anomalous luminescence line emerges concurrently with a red-shift of about 10 meV. While there are various theoretical models addressing the issue of discontinuous red-shift in the quantum Hall regimes, we find that our observation, in its entirety, cannot be explained by the these models.