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Strip plasmons in a two-dimensional electron gas with grounded electrodes

Plasmons in two-dimensional electron gas (2DEG) strips with grounded electrodes (a gate or side contacts) are investigated. We consider two systems: (a) the 2DEG strip with a highly conducting gate and (b) the 2DEG strip with semi-infinite highly conducting side contacts. The systems are described by hydrodynamic equations coupled with the Poisson equation. Dispersion relations and ac electric potential distributions are obtained. We find the plasmon modes whose potential distributions, and hence electron density, are localized to the edges of the strip when the wave number of plasmons in the direction parallel to the strip is large. Frequencies of these strip modes are lower than those of infinite two-dimensional plasmons. The presence of grounded electrode(s) significantly modifies the plasmon dispersion relations.