Drastic Reduction of Plasmon Damping in Two-Dimensional Electron Disks

The plasmon damping has been investigated using resonant microwave absorption of two-dimensional electrons in disks with different diameters. We have found an unexpected drastic reduction of the plasmon damping in the regime of strong retardation. This finding implies large delocalization of retarded plasmon field outside the plane of the two-dimensional electron system. A universal relation between the damping of plasmon polariton waves and retardation parameter is reported.