Charged excitons in fractional quantum Hall regime

We report on photoluminescence experiments carried out at very low temperatures and with magnetic fields up to 28T performed on a high mobility two-dimensional electron gas GaAs/AIGaAs quantum well. Our experiments show that clear signatures of the v =1/3, 2/5, 3/7, 3/5, 2/3, 1 sequence of the FQHE states can also be easily visible even in raw magneto-photoluminescence spectra. Theoretical calculations of excitonic transitions suggest that an explanation of the red shift of emission energy at the Hall plateau boundary may be due to the appearance of additional free charged quasi-particles that bind to an exciton, forming a fractionally charged exciton whose emission energy is expected to be lower, in analogy to well known charged excitons in n-type semiconductors. The magnitude of the shift is a measure of the fractionally charged exciton binding energy. Emission in the insulating state of 2DEG at v = 1/3 is attributed to a neutral quasi-exciton whose complicated energy dispersion results in an emission doublet with its low energy line due to the recombination from excited excitonic states.