Abstract
Abstract The phenomenon of anapole has attracted considerable attention in the field of metamaterials as a possible realization of radiationless objects. We comprehensively study this phenomenon in the cluster-based systems of dielectric particles by considering conditions of anapole manifestation in both single trimers of disk-shaped particles and metamaterial composed on such trimers. Our analytical approach is based on the multipole decomposition method and the secondary multipole decomposition technique. They allow us to associate the anapole with the multipole moments of the trimer and the separate multipole moments of its constitutive particles. The manifestation of anapole in a two-dimensional metamaterial (metasurface) is confirmed by checking the resonant states in the reflected field as well as from the electromagnetic near-field patterns obtained from the full-wave numerical simulation. It is demonstrated that the anapole excitation in trimers results in the polarization-independent suppression of reflection with the resonant enhancement of local electromagnetic fields in the metasurface. Finally, experimental verification of the theoretical results is presented and discussed.
Highlights
The phenomenon of anapole has attracted considerable attention in the field of metamaterials as a possible realization of radiationless objects. We comprehensively study this phenomenon in the cluster-based systems of dielectric particles by considering conditions of anapole manifestation in both single trimers of disk-shaped particles and metamaterial composed on such trimers
Optical features of metamaterials composed of subwavelength dielectric particles can be derived from the single-particle scattering and coupled-mode theory which takes into consideration the interference effects of dynamic multipoles excited in meta-atoms by incoming radiation
For the particles whose scale is less than the effective wavelength of light, the multipole long-wavelength approximation (LWA) [10,11,12] can be applied with inclusion typically of only electric dipole (ED), magnetic dipole (MD), electric quadrupole (EQ), and magnetic quadrupole (MD) moments
Summary
Optical features of metamaterials composed of subwavelength dielectric particles (meta-atoms) can be derived from the single-particle scattering and coupled-mode theory which takes into consideration the interference effects of dynamic multipoles excited in meta-atoms by incoming radiation. An optical anapole arises as a composition of ED and TD moments, which does not produce any far-field radiation due to complete destructive interference of their similar radiation patterns In this state, the near fields appear to be strongly localized inside the particles whereas their radiation to the far zone is significantly suppressed. For the computation of light scattering by nonspherical particles or particles collected into a cluster, full-field simulation techniques should be used Among such techniques, the discrete dipole approximation (DDA), which we use for the present study, allows one to perform calculations of the total extinction, scattering cross-sections (SCS) [43], and multipole contributions for particles of an arbitrary shape [44]. The manifestation of anapole is detected in the near-field patterns and wave transmission and reflection properties for the trimer-based metamaterial in both full-wave numerical simulations and experiment
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