Local far-infrared spectroscopy of edge states in the quantum Hall regime.

Using local spectroscopy, we study the far-infrared response of edge channels in the quantum Hall regime. Both nonresonant and resonant excitations are observed. The resonant signal is shifted with respect to the cyclotron resonance in the two-dimensional electron gas, which reflects the local curvature of the edge potential. The observation of higher-order transitions, which are forbidden in the bulk, reveals the presence of nonparabolic contributions to the edge potential.