Localized plasmons in graphene-coated nanospheres

TL;DR

This paper derives an analytical model for the electromagnetic response of graphene-coated nanospheres, revealing how graphene modifies localized plasmon resonances and providing insights relevant to experimental nanostructures.

Contribution

It extends Mie-Lorenz theory to include conductive graphene coatings, deriving explicit formulas for multipole scattering and plasmon dispersion in spherical geometries.

Findings

Graphene coatings introduce and modify localized plasmons in nanospheres.

Analytical expressions for scattering coefficients and dispersion relations are provided.

Results are applicable to experimentally fabricated graphene nanostructures.

Abstract

We present an analytical derivation of the electromagnetic response of a spherical object coated by a conductive film, here exemplified by a graphene coating. Applying the framework of Mie-Lorenz theory augmented to account for a conductive boundary condition, we derive the multipole scattering coefficients, modified essentially through the inclusion of an additive correction in numerator and denominator. By reductionist means, starting from the retarded response, we offer simple results in the quasistatic regime by analyzing the multipolar polarizability and associated dispersion equation for the localized plasmons. We consider graphene coatings of both dielectric and conducting spheres, where in the former case the graphene coating introduces the plasmons and in the latter case modifies in interesting ways the existing ones. Finally, we discuss our analytical results in the context of extinction cross-section and local density of states. Recent demonstrations of fabricated spherical graphene nanostructures make our study directly relevant to experiments.