Acoustic surface plasmons in the noble metals Cu, Ag, and Au

TL;DR

This study uses self-consistent calculations to reveal the existence and properties of acoustic surface plasmons on noble metal surfaces, showing their dependence on surface-state characteristics and their potential for well-defined low-energy excitations.

Contribution

It demonstrates the presence of acoustic surface plasmons in Cu, Ag, and Au surfaces and analyzes their dispersion, linewidth, and dependence on surface-state orbital decay.

Findings

Acoustic surface plasmons exist on Cu, Ag, and Au (111) surfaces.

These plasmons have linear dispersion at small wave vectors.

They are well-defined up to approximately 400 meV.

Abstract

We have performed self-consistent calculations of the dynamical response of the (111) surface of the noble metals Cu, Ag, and Au. Our results indicate that the partially occupied surface-state band in these materials yields the existence of acoustic surface plasmons with linear dispersion at small wave vectors. Here we demonstrate that the sound velocity of these low-energy collective excitations, which had already been predicted to exist in the case of Be(0001), is dictated not only by the Fermi velocity of the two-dimensional surface-state band but also by the nature of the decay and penetration of the surface-state orbitals into the solid. Our linewidth calculations indicate that acoustic surface plasmons should be well defined in the energy range from zero to $\sim 400$ meV.