Plasmonic excitations in noble metals: The case of Ag

The delicate interplay between plasmonic excitations and interband transitions in noble metals is described by means of ab initio calculations and a simple model in which the conduction electron plasmon is coupled to the continuum of electron-hole pairs. Band-structure effects, especially the energy at which the excitation of the d-like bands takes place, determine the existence of a threshold plasmonic mode, which manifests itself in Ag as a sharp resonance experimentally observed at 3.8 eV. However, such a resonance does not appear in the spectra of the other noble metals. Here this different behavior is also analyzed, and an explanation is provided.