Plasmonic modes in cylindrical nanoparticles and dimers

TL;DR

This paper derives analytical formulas for plasmonic resonance frequencies in cylindrical nanoparticles and dimers, incorporating quantum spill-out effects and analyzing mode coupling and collective excitations.

Contribution

It provides a comprehensive analytical model for plasmonic modes in cylindrical nanoparticles and dimers, including quantum corrections and mode coupling effects.

Findings

Analytical expressions for resonance frequencies of cylindrical nanoparticle modes.

Quantum spill-out effects modify plasmon resonance frequencies.

Mode coupling in dimers leads to bright and dark collective plasmonic modes.

Abstract

We present analytical expressions for the resonance frequencies of the plasmonic modes hosted in a cylindrical nanoparticle within the quasistatic approximation. Our theoretical model gives us access to both the longitudinally and transversally polarized dipolar modes for a metallic cylinder with an arbitrary aspect ratio, which allows us to capture the physics of both plasmonic nanodisks and nanowires. We also calculate quantum mechanical corrections to these resonance frequencies due to the spill-out effect, which is of relevance for cylinders with nanometric dimensions. We go on to consider the coupling of localized surface plasmons in a dimer of cylindrical nanoparticles, which leads to collective plasmonic excitations. We extend our theoretical formalism to construct an analytical model of the dimer, describing the evolution with the inter-nanoparticle separation of the resultant bright and dark collective modes. We comment on the renormalization of the coupled mode frequencies due to the spill-out effect, and discuss some methods of experimental detection.