New results on the magneto-luminescence of a two-dimensional electron gas around integer filling factors

The magneto-photoluminescence emission of a high mobility electron gas in a GaAs/GaAlAs single hetero-structure shows a remarkable behavior near filling factor 2. The emission of the electron gas starts abruptly at ν=2 in a field range narrower than 1 mT and shows a hysteresis cycle of 25-30 mT. At low temperatures the emission energy remains essentially field-independent below ν=2 up to a critical magnetic field. Beyond it, the emission peak tends progressively to the usual Landau-level-like behavior. Well-defined dips in the peak intensity and in its circular polarization degree at the critical field indicate an instability of the electron system and its transition to a different state. All these effects disappear when the temperature is raised from 300 mK to 5 K. Transport measurements indicate that the critical field corresponds to the onset of extended states at the Fermi level. Although the full understanding of the reported behavior requires a detailed theoretical calculation, the results are qualitatively interpreted as due to the formation of complex bound-states with the photo-created hole. The results are presented in the context of the recent activity in the field, and some possible trends for future development are given.