Optical probing of lowest Landau level neutral collective excitations in fractional quantum Hall fluids

Low-lying collective neutral excitations of fractional quantum Hall (FQH) fluids would provide key examinations of strongly correlated electronic phases, which could be detected by precise optical methods (e. g. photoluminescence (PL) and resonant inelastic light scattering (RILS)) at milli-Kelvins. Here, we report initial experimental results of probing the long-wavelength gap excitations and roton modes around filling factor v=1/3 in a single GaAs quantum well with ultra-high electron mobility, through circular polarized RILS. Excitations involving spin degree of freedom as an indicator of the interactions and polarization of FQH fluids are found to be subject to multiple resonances. We discuss that they correspond to an unexpected large number of transitions in PL. Selective enhancement of collective excitations at resonance would enrich the insights on incompressible quantum liquids in the regime of the FQH effect.