Abstract
The plasmon hybridization theory is based on a quasi-electrostatic approximation of the Maxwell’s equations. It does not take into account magnetic interactions, retardation effects, and radiation losses. Magnetic interactions play a dominant role in the scattering from dielectric nanoparticles. The retardation effects play a fundamental role in the coupling of the modes with the incident radiation and in determining their radiative strength; their exclusion may lead to erroneous predictions of the excited modes and of the scattered power spectra. Radiation losses may lead to a significant broadening of the scattering resonances. We propose a hybridization theory for non-Hermitian composite systems based on the full-Maxwell equations that, overcoming all the limitations of the plasmon hybridization theory, unlocks the description of dielectric dimers. As an example, we decompose the scattered field from silicon and silver dimers, under different excitation conditions and gap-sizes, in terms of dimer modes, pinpointing the hybridizing isolated-sphere modes behind them.
Highlights
The description of the electromagnetic scattering from nanostructures in terms of their resonances and modes is essential for both the analysis and the engineering of the field-matter interaction
We investigate the hybridization mechanism in silver and silicon dimers for the modes that are excited in the scattering under longitudinal and transverse plane-wave excitations
We have investigated the modes and resonances in the electromagnetic scattering from a dimer of spheres by using the full-Maxwell equations and the material independent modes
Summary
The description of the electromagnetic scattering from nanostructures in terms of their resonances and modes is essential for both the analysis and the engineering of the field-matter interaction. The material-independent modes allow separating the role of geometry, material, and incident electromagnetic field; provide fundamental information on the resonant electromagnetic behaviour of bodies that other approaches hide They are not orthogonal in the usual sense but, unlike quasi-normal modes, they satisfy the radiation condition at infinity. Regardless of the chosen definition, the electromagnetic modes of composite electromagnetic structures can be extremely complicated They exhibit a complex dependence on the geometry of the constituent parts and on their spatial arrangement. The theory of plasmon hybridization[18] is grounded in the electrostatic theory: it is based on compact hermitian operators and orthogonal electric field modes This theory is only applicable to metal structures much smaller than the incident wavelength, because the magnetic interactions and the radiation effects are absent. Its validity domain can be extended to include weak radiative contributions by using perturbation approaches[24] or by adding retardation to the Coulomb potential[25], it completely fails to describe dielectric resonators, which are dominated by magnetic interactions[26]
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