Dependence of the Normal Modes of Plasma Oscillation at a Bimetallic Interface on the Electron Density Profile

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Abstract
Using the high-frequency expansion of the random-phase approximation, we study the normal modes of plasma oscillations at a bimetallic interface. We find that the surface plasmons decay by damping into bulk oscillations of the low-density metal, whose wavelength becomes shorter as the low-density-side density decreases. If the low-density-side electron density is less than approximately a third that on the high-density side, the high-frequency expansion fails because the surface plasmons begin to decay into individual particle-hole states. Thus we are unable to use this expansion to study the modes at metal-vacuum interfaces, where the low-density-side electron density is zero. For bimetallic systems that allow the high-frequency expansion, we show how to determine the dependence of the plasmon dispersion relations on the density profile and stress tensor.