Nonradiating anapole modes in dielectric nanoparticles

TLDR

Nonradiating current configurations, such as the anapole—a superposition of electric and toroidal dipoles that destructively cancels far‑field radiation—have long attracted physicists and provide a platform for studying exotic electromagnetic phenomena at optical frequencies. The study experimentally demonstrates that dielectric nanoparticles can support a radiationless anapole mode in the visible spectrum. By tuning the nanoparticle geometry to align the toroidal and electric dipole resonances, the authors create a pronounced far‑field scattering dip and a characteristic near‑field pattern indicative of the anapole. The experiment reveals a pronounced far‑field scattering dip and a distinctive near‑field distribution, confirming the presence of the anapole mode.

Abstract

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.