Plasmon dispersion in metal nanoparticle chains from angle-resolved scattering

TL;DR

This study measures the plasmon dispersion in metal nanoparticle chains using angle-resolved scattering, revealing the importance of far-field interactions and implications for nanocircuit design.

Contribution

It provides experimental dispersion data for Ag and Au nanoparticle chains, highlighting the significance of retarded far-field interactions over electrostatic models.

Findings

Large transverse and longitudinal mode splitting observed

Far-field retarded interactions dominate over electrostatic models

Implications for nanocircuit design with coherent far-field coupling

Abstract

We present angle and frequency resolved optical extinction measurements to determine the dispersion relation of plasmon modes on Ag and Au nanoparticle chains with pitches down to 75 nm. The large splitting between transverse and longitudinal modes and the band curvature are inconsistent with reported electrostatic near-field models, and confirm that far-field retarded interactions are important, even for $\lambda/5$-sized structures. The data imply that lower propagation losses, larger signal bandwidth and larger maximum group velocity then expected can be achieved for wave vectors below the light line. We conclude that for the design of optical nanocircuits coherent far-field couplings across the entire circuit need to be considered, even at subwavelength feature sizes.