Comparative Study of Light Guiding by Freestanding Linear Chains of Spherical Au and Si Nanoparticles

Electromagnetic energy guiding by free-standing straight finite chains of Au and Si spherical nanoparticles is comparatively studied on the basis of a system of integral equations for self-consistent currents excited inside particles. Self-consistent currents are given in terms of an electric field T-scattering tensor (dyadic) operator of a single particle of any shape. Simplifying the T-scattering operator, the equations system is resolved analytically in the nearest-neighbor coupling approximation. Interactions beyond the nearest neighbors are accounted for by the perturbative theory. It is shown that electromagnetic excitation propagates along a chain of coupled particles without radiation losses in the form of a dark mode. The resonant conditions for the coupling parameter yield the frequency of the dark mode and the corresponding radius of the particles. As a result, unlike Au chains, no long-range electromagnetic energy transfer was revealed along the Si chains. Physically, in both cases of Au and Si spheres, the resonant frequencies fall within the bands of the corresponding electric dipole Mie resonances. However, the positive value of the real part of the Si refraction index at the resonant frequency causes exponential excitation currents decreasing with the particle number.