Surface plasmons at composite surfaces with diffusive charges

TL;DR

This paper develops a model for surface plasmons on composite metal surfaces with diffusive charges, resolving boundary condition issues and matching experimental data on plasmon dispersion and linewidth.

Contribution

It introduces a Boltzmann equation approach to handle boundary conditions involving localized and continuous charges, explaining plasmon behavior on disordered or nanostructured surfaces.

Findings

Model accurately describes a variety of SP dispersions.

Surface plasmon linewidth depends on charge scattering strength.

The approach aligns well with experimental observations.

Abstract

Metal surfaces with disorder or with nanostructure modifications are studied, allowing for a localized charge layer (CL) in addition to continuous charges (CC) in the bulk, both charges having a compressional or diffusive non-local response. The notorious problem of "additional boundary conditions" is resolved with the help of a Boltzmann equation that involves the scattering between the two charge types. Depending on the strength of this scattering, the oscillating charges can be dominantly CC or CL; the surface plasmon (SP) resonance acquires then a relatively small linewidth, in agreement with a large set of data. With a few parameters our model describes a large variety of SP dispersions corresponding to observed data.