The normal modes at the surface of simple metals

Abstract

The dynamic response of the electrons at the surface of simple metals, like Na, K and Cs, to an external time varying field is discussed in this paper. Of special interest are the normal modes at a surface, defined theoretically by the poles in the reflection function. The surface plasmon is the best known normal mode of the electrons at the surface, but theory has predicted other normal modes. Recently a new mode, called a Multipole Plasmon Mode, has been observed in inelastic electron scattering experiments. The origin and physical properties of this Multipole Mode as well as the Surface Plasmon Mode will be described.