Spin excitations at $\nu >1/3$: a probe of composite fermions interactions

We present a resonant inelastic light scattering study of spin excitations at filling factors of the fractional quantum Hall effect (FQHE) with $\nu >1/3$, in which composite fermions may condense into higher order quasiparticles. Observations of low lying spin excitations enable us to study the composite fermions (CF) Landau level configuration and the impact of CF residual interactions at filling factors away from the major FQHE sequences. A very low energy spin mode ($\omega\leq0.1~meV$), which displays a marked temperature dependence above T$\sim$100~mK, emerges at filling factors close to $\nu=4/11$ and remains with small changes in energy in the filling factor range $4/11\leq\nu\leq5/13$. The spectral intensity of this spin excitation becomes negligible at temperatures above 300~mK. The marked temperature dependence of the intensity suggest the existence of even lower excitation modes at energies well below 0.1~meV. We discuss the implication of these experiments on the possibility of higher order CF suggested by transport measurements at $\nu=$4/11. \\ This work is supported by the NSF under Award Number DMR-03-52738 and by the DoE award DE-AIO2-04ER46133. It is also supported by a research grant of the W. M. Keck Foundation.