Spin waves in the second Landau level: Probing the spin-polarization enigma*

The physics in the second Landau level (SLL) is governed by competing phases resulting in striking phenomena. We use resonant inelastic light scattering experiments to explore collective excitation modes with the focus on low lying spin excitation modes in the SLL. The intensity of the small momentum spin-wave at the bare Zeeman energy (E$_{Z})$ collapses for filling factors away from integer filling factor $\nu <$3 and are dominated by a continuum of modes. We find that at the fractional filling factors 14/5, 8/3, 5/2, 7/3, 11/5 the continuum coexists with a weak but distinct signal at E$_{Z}$, a long wavelength spin-wave that suggests a degree of spin polarization. In addition, at 5/2 an intriguing well developed sharp mode is observable below E$_{Z}$, which is unique for the even-denominator filling factor. Modes at energies larger than E$_{Z}$ merge additionally at odd-denominator states in ILS spectra, most pronounced for 7/3, in a manner that is similar to that of the 1/3 state. This observation could be evidence that the CF framework could be applicable to these states.