Plasmonic Waves on a Chain of Metallic Nanoparticles: Effects of a Liquid Crystalline Host or an Applied Magnetic Field

TL;DR

This paper investigates how anisotropic environments and magnetic fields influence plasmonic wave propagation along metallic nanoparticle chains, revealing tunable dispersion relations and polarization effects relevant for nanophotonic applications.

Contribution

It introduces a detailed analysis of how liquid crystalline hosts and magnetic fields modify plasmonic wave dispersion and polarization in nanoparticle chains, including effects like Faraday rotation.

Findings

Dispersion relations are significantly altered by anisotropic hosts.

Magnetic fields induce circular polarization and Faraday rotation.

Anisotropy and magnetic fields enable control of plasmonic wave properties.

Abstract

A chain of metallic particles, of sufficiently small diameter and spacing, allows linearly polarized plasmonic waves to propagate along the chain. In this paper, we consider how these waves are altered by an anisotropic host (such as a nematic liquid crystal) or an applied magnetic field. In a liquid crystalline host, with principal axis (director) oriented either parallel or perpendicular to the chain, we find that the dispersion relations of both the longitudinal ($L$) and transverse ($T$) modes are significantly altered relative to those of an isotropic host. Furthermore, when the director is perpendicular to the chain, the doubly degenerate $T$ branch is split by the anisotropy of the host material. With an applied magnetic field ${\bf B}$ parallel to the chain, the propagating transverse modes are circularly polarized, and the left and right circularly polarized branches have slightly different dispersion relations. As a result, if a linearly polarized transverse wave is launched along the chain, it undergoes Faraday rotation. For parameters approximating that of a typical metal and for a field of 2T, the Faraday rotation is of order 1$^o$ per ten interparticle spacings, even taking into account single-particle damping. If ${\bf B}$ is perpendicular to the chain, one of the $T$ branches mixes with the $L$ branch to form two elliptically polarized branches. Our calculations include single-particle damping and can, in principle, be generalized to include radiation damping. The present work suggests that the dispersion relations of plasmonic waves on chain of nanoparticles can be controlled by immersing the chain in a nematic liquid crystal and varying the director axis, or by applying a magnetic field.