Local-field effects on the near-surface and near-interface screened electric field in noble metals

The screening of an optical electric field at a noble metal surface is evaluated within a semiclassical model where the nonlocality of the d-electron response is taken into account via a set of interacting atomic dipoles. The dipole moments in the first few atomic layers differ from the expected bulk value due to the symmetry breakdown at the surface. These effects give rise to surface-induced electric charges and currents and to a surface-induced electric field which vanishes in the bulk but can be important in the top atomic layers. This field takes into account local-field effects, is frequency dependent and is strongly enhanced in a frequency range characteristic of the metal surface. Results are first given for an electric field perpendicular to the metal surface, and the enhancement of the surface response is mainly due to interband electronic transitions for the Cu and Au surfaces, while it originates from a coupling with the bulk plasmon excitations for an Ag surface. The anisotropy in the surface response is studied for an electric field parallel to the anisotropic Ag(110) surface. Finally, the calculation is generalized to describe screening effects at an interface between two different noble metals. The simple surface model used in this paper shows that the surface-induced electric field should be taken into account in the simulations of surface spectroscopy, where the calculated signal directly depends on the linearly screened field at the surface.