Electromagnetic dynamical characteristics of a surface plasmon-polariton

TL;DR

This paper derives explicit, singularity-free expressions for the electromagnetic energy, momentum, and angular momentum densities of surface plasmon-polaritons at media interfaces, incorporating dispersion effects and linking to magnetization phenomena.

Contribution

It provides a comprehensive, dispersion-aware theoretical framework for analyzing the electromagnetic characteristics of SPPs, including spin and orbital momenta, with implications for magnetization effects.

Findings

Explicit formulas for energy and momentum densities of SPPs

Identification of a localized surface spin momentum component

Connection between SPP spin momentum and magnetization current

Abstract

We consider the electromagnetic field near an interface between two media with arbitrary real frequency-dependent permittivities and permeabilities, under conditions supporting the surface plasmon-polariton (SPP) propagation. The dispersion of the electric and magnetic properties is taken into account based on the recent approach for description of the spin and momentum of electromagnetic field in complex media [Phys. Rev. Lett. 119, 073901 (2017); New J. Phys., 19, 123014 (2017)]. It involves the Minkowski momentum decomposition into the spin and orbital parts with the dispersion-modified permittivities and permeabilities. Explicit expressions are derived for spatial densities of the energy, energy flow, spin and orbital momenta and angular momenta of the transverse-magnetic (TM) SPP field. They are free from non-physical singularities; the only singular contribution describes a strictly localized surface part of the spin momentum that can be associated with the magnetization current in the conductive part of the SPP-supporting structure. On this ground, a phenomenological theory of the SPP-induced magnetization (predicted earlier based on the simplified microscopic approach) is outlined. Possible modifications and generalizations, including the transverse-electric (TE) SPP waves, are discussed.