Plasmonic modes in nanowire dimers: A study based on the hydrodynamic Drude model including nonlocal and nonlinear effects

TL;DR

This paper investigates plasmonic modes in nanowire dimers using a nonlinear, nonlocal hydrodynamic Drude model, revealing how nonlocality and symmetry influence field distributions and second-harmonic generation efficiencies.

Contribution

It combines analytical and numerical methods to analyze plasmonic modes with nonlocal and nonlinear effects, providing new insights into mode classification and enhancement of second-harmonic generation.

Findings

Nonlocality significantly affects field distributions and spectra.

Symmetry considerations enable enhanced second-harmonic generation.

Analytical classification aids understanding of mode excitation mechanisms.

Abstract

A combined analytical and numerical study of the modes in two distinct plasmonic nanowire systems is presented. The computations are based on a Discontinuous Galerkin Time-Domain approach and a fully nonlinear and nonlocal hydrodynamic Drude model for the metal is utilized. In the linear regime, these computations demonstrate the strong influence of nonlocality on the field distributions as well as on the scattering and absorption spectra. Based on these results, second-harmonic generation efficiencies are computed over a frequency range that covers all relevant modes of the linear spectra. In order to interprete the physical mechanisms that lead to corresponding field distributions, the associated linear quasi-electrostatic problem is solved analytically via conformal transformation techniques. This provides an intuitive classification of the linear excitations of the systems that is then applied to the full Maxwell case. Based on this classification, group theory facilitates the determination of the selection rules for the efficient excitation of modes, both in the linear and the nonlinear regime. This leads to significantly enhanced second-harmonic generation via judiciously exploiting the system symmetries. These results regarding the mode structure and second-harmonic generation are of direct relevance to other nano-antenna systems.