Figure 1

(a) Comparison of light scattering spectra taken at similar values of $B_T$ at filling factor $\nu \to 1/2$. The gray line is from sample S1 at $\theta =50°$, and the black line is from sample S2 with $\theta =30°$. The experimental geometry is depicted in the inset. (b) Same spectra as in (a) for sample S1 (gray line). The thick black line corresponds to the spectrum with the laser subtracted. The dotted line corresponds to a fit of the laser. The thin black line is a Lorentzian fit to the spin wave, and the shadowed gray area corresponds to the contribution from the spin-flip mode. The inset displays a spectrum for sample S1 at $\theta =40°$ (black line). The gray line corresponds to a fit to the contribution of the spin wave and the dotted line to the laser. Low energy contributions arising from the spin-flip mode are observed.Reuse & Permissions

Figure 2

Representation of CF energy levels and lowest spin-flip (SF) transitions for filling factor $\nu \to 1/2$. Populated levels are shown in black and empty ones in gray. (a) Fully spin-polarized state. (b) State with partial spin polarization. The lowest SF transition is indicated by an arrow from the highest occupied state to the lowest unoccupied one of the opposite spin. For $\nu \to 1/2$ the SF transition energy collapses for partial spin polarization in (b).Reuse & Permissions

Figure 3

Low energy light scattering spectra at $1/2>\nu \ge 3/7$. The gray line is sample S1 at 50°. Black lines are sample S2 at 30°. Excitations labeled SF at $\nu =3/7$ and $\nu =4/9$ correspond to the roton of the lowest SF mode. The arrows point to the maximum in the contribution of the SF mode.Reuse & Permissions

Figure 4

Energies of low-lying spin excitations for the filling factor range $2/5\le \nu <1/2$ (a) sample S1 at 50° and (b) sample S2 at 30°. The squares correspond to the $q\to 0$ limit of the spin wave and the bars to the contributions of the SF modes. The hatched regions at the bottom of both panels correspond to the energies not accessible in our experiments because of the elastic light scattering of the incident laser beam that is seen as an intense peak centered at zero energy shift.Reuse & Permissions