Nonradiating anapole modes in dielectric nanoparticles.

Andrey E Miroshnichenko,Boris Luk’Yanchuk,Yuri S Kivshar,Ye Feng Yu,Andrey B Evlyukhin,Arseniy I Kuznetsov,Reuben M Bakker,Arkadi Chipouline,Boris N Chichkov

doi:10.1038/ncomms9069

Abstract

Nonradiating current configurations attract attention of physicists for many years as possible models of stable atoms. One intriguing example of such a nonradiating source is known as ‘anapole'. An anapole mode can be viewed as a composition of electric and toroidal dipole moments, resulting in destructive interference of the radiation fields due to similarity of their far-field scattering patterns. Here we demonstrate experimentally that dielectric nanoparticles can exhibit a radiationless anapole mode in visible. We achieve the spectral overlap of the toroidal and electric dipole modes through a geometry tuning, and observe a highly pronounced dip in the far-field scattering accompanied by the specific near-field distribution associated with the anapole mode. The anapole physics provides a unique playground for the study of electromagnetic properties of nontrivial excitations of complex fields, reciprocity violation and Aharonov–Bohm like phenomena at optical frequencies.

Highlights

Nonradiating current configurations attract attention of physicists for many years as possible models of stable atoms
The classical analogue of a stationary anapole is the well-known toroid with a constant poloidal surface current[4]. This current distribution is associated with a toroidal dipole moment pointing outward along the torus symmetry axis
The existence of toroidal multipoles is required by the symmetry of the order parameters with respect to the inversions of space and time: in addition to the well-known electric polarization and magnetization (r-even and t-odd axial vector), there should be the order parameters described by an r- and t-even polar vector and an r- and t-odd axial vector[11]

Summary

Introduction

Nonradiating current configurations attract attention of physicists for many years as possible models of stable atoms. We observe a strong suppression of the far-field scattering along with nontrivial evolution of the electromagnetic field inside a nanodisk close to the wavelength of the anapole mode excitation.

Results

Conclusion