Observation of Collective Excitations of the Dilute 2D Electron System
Abstract
We report inelastic light scattering measurements of dispersive spin and charge density excitations in dilute 2D electron systems reaching densities less than 1010 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 rs is increased. Instead of a soft mode instability predicted by Hartree--Fock calculations for rs ~ 3.3, we find evidence of multiple rotons in the dispersion of the softening spin excitations. Extrapolation of the data indicates the possibility of an instability for rs >~ 11.
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