title: Electromagnetic toroidal excitations in matter and free space.
abstract: The toroidal dipole is a localized electromagnetic excitation, distinct from the magnetic and electric dipoles. While the electric dipole can be understood as a pair of opposite charges and the magnetic dipole as a current loop, the toroidal dipole corresponds to currents flowing on the surface of a torus. Toroidal dipoles provide physically significant contributions to the basic characteristics of matter including absorption, dispersion and optical activity. Toroidal excitations also exist in free space as spatially and temporally localized electromagnetic pulses propagating at the speed of light and interacting with matter. We review recent experimental observations of resonant toroidal dipole excitations in metamaterials and the discovery of anapoles, non-radiating charge-current configurations involving toroidal dipoles. While certain fundamental and practical aspects of toroidal electrodynamics remain open for the moment, we envision that exploitation of toroidal excitations can have important implications for the fields of photonics, sensing, energy and information.
authors.affiliation: Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK.
authors.forename: N
authors.initials: N
authors.lastname: Papasimakis
authors.affiliation: Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK.
authors.forename: V A
authors.initials: VA
authors.lastname: Fedotov
authors.affiliation: Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK.
authors.forename: V
authors.initials: V
authors.lastname: Savinov
authors.affiliation: Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK.
authors.forename: T A
authors.initials: TA
authors.lastname: Raybould
authors.affiliation: Optoelectronics Research Centre &Centre for Photonic Metamaterials, University of Southampton, Highfield SO17 1BJ, UK.|TPI and Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637378, Singapore.
authors.forename: N I
authors.initials: NI
authors.lastname: Zheludev
mesh_terms: D001105:Archaea; D019843:Archaeal Proteins / Q000737:chemistry; D001672:Biocompatible Materials / Q000737:chemistry*; D003198:Computer Simulation; D055590:Electromagnetic Phenomena; D004912:Erythrocytes; D008420:Manufactured Materials; D008422:Materials Testing; D055095:Optics and Photonics / Q000295:instrumentation
chemical_list: D019843:Archaeal Proteins; D001672:Biocompatible Materials