Anomalous magneto-optical emission of a two-dimensional electron gas below filling factor 2

The magneto-photoluminescence emission of a high mobility electron gas in a GaAs/AlGaAs single heterostructure shows an extremely abrupt onset at filling factor v=2. At higher fields the energy of the emission peak remains essentially field-independent up to a critical field value, beyond which it converges to the usual Landau-like behavior. Well-defined dips in the peak intensity and in its circular polarization degree at this critical field may be related to a change in the electronic interaction, possibly related to the formation of an excitonic complex of the photogenerated holes and the electron gas. All these effects tend to disappear when the temperature is raised from 0.3 K to 2 K.