View source for Physics:Anapole

{{Short description|System of currents that do not not radiate into the far field}}
In [[Physics:Physics|physics]], an '''anapole''' ({{ety|el|''ἀνά'' (ana)|above||''πόλος'' (polos)|pole}}) is a system of [[Physics:Electric current|currents]] that does not radiate into the [[Physics:Near and far field|far field]]. The term "anapole" first appeared in the work of [[Biography:Yakov Zeldovich|Zel'dovich]], in which he thanks [[Biography:Alexander Kompaneyets|A. S. Kompaneets]], who first proposed the name.<ref>Zel’Dovich, I. B. (1958). Electromagnetic interaction with parity violation. Sov. Phys. JETP, 6(6), 1184-1186.</ref>

An anapole is a system of currents that transforms under all transformations of the symmetry group [[Orthogonal group|O(3)]] as a certain multipole (or the corresponding [[Vector spherical harmonics|vector spherical harmonic]]), but does not radiate to the [[Physics:Near and far field|far field]].

== Photonics ==
[[File:Anapoles.png|thumb|[[Physics:Mie scattering|Mie scattering]] by a dielectric nanoparticle with refractive index n=4.5. Normalized scattering cross-section spectrum in linear and log scale. Zeros, which refer to anapole states, are marked.]]
In photonics, anapoles first appeared in 2015<ref>Miroshnichenko, Andrey E., et al. "Nonradiating anapole modes in dielectric nanoparticles." Nat. Commun., vol. 6, no. 8069, 27 Aug. 2015, pp. 1-8, doi:10.1038/ncomms9069.</ref> as zeros in the Mie-coefficient of a particular multipole in the scattering spectrum. They can also be explained as destructive interference of a "cartesian multipole" and a "[[Physics:Toroidal moment|toroidal]] multipole". The anapole state is not an eigenmode. Total scattering cross-section is not zero in the anapole state, due to the contribution of other multipoles.<ref>Zenin, Vladimir A., et al. "Direct Amplitude-Phase Near-Field Observation of Higher-Order Anapole States." Nano Lett., vol. 17, no. 11, 8 Nov. 2017, pp. 7152-9, doi:10.1021/acs.nanolett.7b04200.</ref><ref>Baryshnikova, Kseniia V., et al. "Optical Anapoles: Concepts and Applications." Adv. Opt. Mater., vol. 7, no. 14, 1 July 2019, p. 1801350, doi:10.1002/adom.201801350.</ref>

The terms "anapole" and [[Physics:Toroidal moment|toroidal moment]] were once used synonymously,<ref>Lewis, Robert R. "Anapole moment of a diatomic polar molecule." Physical Review A 49.5 (1994): 3376.</ref><ref>Popov, A. I., D. I. Plokhov, and A. K. Zvezdin. "Anapole moment and spin-electric interactions in rare-earth nanoclusters." Europhysics Letters 87.6 (2009): 67004.</ref> but this ended.

==See also==

* [[Physics:Toroidal moment|Toroidal moment]]

==References==
{{Reflist}}


[[Category:Electric current]]
[[Category:Electromagnetic radiation]]
[[Category:Photonics]]

{{Sourceattribution|Anapole}}