Crossover from proximity to ordinary two-dimensional plasma excitation

Abstract

We have investigated plasma excitations in a disk-shaped two-dimensional electron system (2DES), the edge of which was covered by an overlaying metallic gate. We have found that the microwave response of the structure is dominated by the proximity plasma mode propagating along the disk edge. Significantly, we find that as the overlap between the 2DES and the gate tends to zero, the frequency of the proximity plasmon makes a transition to that of an ordinary 2D plasmon in the ungated area of the 2DES. We also observe that tuning the electron density under the gate results in a crossover from the proximity to the laterally screened 2D plasmon. The experimental findings are analyzed using the plasmonic lumped-element approach.