Plasmon dispersion in two-metal systems

Abstract

The hydrodynamic model incorporating spatial dispersion is used to investigate the nonretarded plasmon dispersion for a bimetallic interface and for two arbitrary metal half-spaces separated by a vacuum. For the bimetallic interface, the full curve for the well known interface plasmon, starting at omega 2=1/2( omega p12+ omega p22), is given. It is shown that a similar plasmon mode exists when the metals are cleaved and separated, but which corresponds to a different form of density fluctuation and has a dependence on the separation distance. In addition, a new 'image' plasmon omega im is predicted. This arises from the image of the denser metal 2 ( omega p2> omega p1) forming as a result of the density response of the bulk electrons in metal 1, and is independent of the parameters of the less dense metal. The generalisations of the well known symmetric ( omega +) and antisymmetric ( omega -) surface plasmons, seen for two identical metals, are also derived. The generalised upper branch omega + only appears if omega p1> omega p2/ square root 2 and forms the continuation of omega im below the bulk continuum region of the less dense metal.