Observation of the logarithmic dispersion of high-frequency edge excitations

We report phase sensitive measurements of microwave propagation through a high mobility two dimensional electron gas subjected to a perpendicular magnetic field. Two types of configurations were used, one that allows all wave vectors q, and one that selects only specific q values. The spectrum of edge excitations was studied over a broad frequency span, which allowed us to observe the logarithmic dispersion of edge magneto-plasmons.