ANISOTROPY OF SURFACE-PLASMONS IN METALS

In this paper we propose a phenomenological model to explain the aniso tropy in the dispersion of surface plasmons, which we suggest to be re lated also to the different effective mass of the electrons involved i n the excitation. The model is applied to silver surfaces where a larg e set of experimental data exists, obtaining a good qualitative agreem ent with experiment. The damping of the surface plasmons is also discu ssed. Again in agreement with the experimental results, a linear depen dence on temperature and momentum transfer is found for the linewidth. The anisotropy of the latter is then determined by the anisotropy of the effective mass and of the relaxation time of the electrons in the surface region, tau(surf), and is small only if tau(surf) approximate to tau(bulk).