Excitation spectra of unconventional FQHE states in the SLL from Light Scattering Experiments*

The fascinating interaction physics in the second Landau level (SLL) supports the emergence of exotic quantum phases and unconventional possibly FQHE states such as e.g. at $\nu =$ 5/2 and 2$+$1/3 and the weaker state at $\nu =$ 2$+$3/8 and 2$+$2/5. We observe clear signatures for gapped collective excitations in inelastic light scattering experiments just for these `magic' filling factors and only for low temperatures substantiating access to the physics of the incompressible quantum fluids [1]. The lowest excitation feature in the spectrum at 2$+$1/3 occurs at around 70 $\mu $eV. The analysis of spectral lineshapes suggests magnetoroton features that are characteristic of 2D neutral excitations in a perpendicular magnetic field. The striking polarization dependence observable in light scattering experiments in the SLL are consistent with nematic FQHE states. [1] U. Wurstbauer \textit{et al.}, arXiv:1507.04939v2 (2015).