Plasmonic mode evolution in rotated aluminum nanorod chains: A symmetry-breaking analysis

Abstract

The collective optical response of plasmonic nano-assemblies is fundamentally governed by the interplay between near-field coupling, geometric configuration, and the intrinsic dielectric properties of the constituent materials. This study presents a comprehensive computational analysis of the optical cross-sections (absorption, scattering, extinction) and near-field properties of linear chains of 10 aluminum nanorods with fixed diameter $D=20\mathrm{nm}$ and length $L=100\mathrm{nm}$. By systematically deconstructing the spectral response as a function of two distinct rotational schemes — an inter-element azimuthal rotation and a global orientational rotation — we elucidate the evolution and tunability of plasmonic modes. Analysis of the surface charge density provides direct visualization of the underlying physics, confirming the nature of collective bonding modes and the mechanism by which internal symmetry breaking geometrically activates otherwise inaccessible individual-rod longitudinal modes, and contrasting it with the simple projection mechanism of external rotation. We demonstrate that while inter-particle separation dictates the foundational energy of the hybridized modes, inter-element rotation acts as a continuous geometric modulator of the accessible mode structure. Throughout this analysis, it is established that absorption is the dominant energy dissipation channel, a direct consequence of the high intrinsic ohmic losses in aluminum.