Plasma waves in a two-dimensional electron system laterally screened by a metallic gate

The dispersion of magnetoplasma and plasma excitations in two-dimensional electron systems, whose edges are formed by a voltage applied to a metallic gate, has been studied. A substantial decrease in the plasma wave frequency as compared to the plasma frequency measured in the etched mesas with the same geometry, size, and electron density has been observed. The dependence of the observed frequency softening on the structure size has been studied and the laterally screened plasma excitation has been shown to violate the square-root dispersion relation.