Collective excitations in the dilute 2D electron system

We report inelastic light scattering measurements of dispersive spin and ch arge density excitations in dilute 2D electron systems reaching densities l ess than 10(10) cm(-2). In the quantum Hall state at nu = 2, roton critical points in the spin inter-landau level mode show a pronounced softening as r(s) is increased. Instead of a soft mode instability predicted by Hartree- Fock calculations for r(s) similar to 3.3, we find evidence of multiple rot ons in the dispersion of the softening spin excitations.