Abstract
We report the observation of low frequency collective excitations of the two-dimensional electron system in a GaAs/GaAlAs heterojunction in a magnetic field. The excitations are present for temperatures less than 2 K and fields corresponding to filling factors between
ν =
1
2
and ν = 7
. Their dispersion relation is linear in the wave vector
k, and shows no evidence of a gap. These modes vanish between the Hall plateaus and elsewhere their propagation velocity follows a
H
−1 1n(
αH) field dependence. The features of these modes are consistent with a propagating perimeter wave in a quantum 2D Coulomb system.