Magnetoplasma modes of the two-dimensional electron gas at nonintegral filling factors

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Abstract
Two approaches are used to discuss the collective excitations of a two-dimensional electron gas in a perpendicular magnetic field B, which occur at energies near ħωc=ħeB/mc. The first approach, a time-dependent Hartree-Fock approximation, becomes exact at integral Landau-level filling in the strong-field limit. The second approach, a generalized single-mode approximation, incorporates the strong correlations among electrons in a partially filled Landau level and is more reliable but can be conveniently implemented only in the strong-field limit. Both approaches predict the existence of poles in the density response function at finite wave vector for ω=ωc, which may lead to anomalies in the cyclotron-resonance line shape.