Optical probing of electronic fractional quantum Hall states

We report on the observation of a fine structure in the photoluminescence emission of high-mobility GaAs/AlGaAs single heterojunctions in the fractional quantum Hall regime. A splitting of the emission band into three lines is found both at filling factor ν=2/3 and in the region 2/5>ν>1/3. The dependencies on filling factor, electron density, and temperature show that the fine structure arises from the recombination of fractionally charged elementary excitations of the two-dimensional electron liquid and an itinerant valence-band hole. These quasiparticle excitations (anyon excitons) exhibit a dispersion relation with an absolute minimum at large momentum, leading to a characteristic, broad emission band at the low-energy side of the photoluminescence spectrum around ν=1/3.