Abstract-Optical Anapole Metamaterial

Pin Chieh Wu, Chun Yen Liao, Vassili Savinov, Tsung Lin Chung, Wei Ting Chen, Yao-Wei Huang, Pei Ru Wu, Yi-Hao Chen, Ai-Qun Liu, Nikolay I. Zheludev,  Din Ping, Tsai

http://pubs.acs.org/doi/abs/10.1021/acsnano.7b08828

The toroidal dipole is a localized electromagnetic excitation independent from the familiar magnetic and electric dipoles. It corresponds to currents flowing along minor loops of a torus. Interference of radiating induced toroidal and electric dipoles leads to anapole, a non-radiating charge-current configuration. Interactions of induced toroidal dipoles with electromagnetic waves have recently been observed in artificial media at microwave, terahertz and optical frequencies. Here, we demonstrate a quasi-planar plasmonic metamaterial – a combination of dumbbell aperture and vertical split-ring resonator - that exhibits transverse toroidal moment and resonant anapole behavior in the optical part of the spectrum upon excitation with a normally incident electromagnetic wave. Our results prove experimentally that toroidal modes and anapole modes can provide distinct and physically significant contributions to the absorption and dispersion of slabs of matter in the optical part of the spectrum in conventional transmission and reflection experiments.

Abstract-Sharp Toroidal Resonances in Planar Terahertz Metasurfaces

http://onlinelibrary.wiley.com/doi/10.1002/adma.201601611/abstract

A toroidal dipole in metasurfaces provides an alternate approach for the excitation of high-Qresonances. In contrast to conventional multipoles, toroidal dipole interaction strength depends on the time derivative of the surrounding electric field. A characteristic feature of a toroidal dipole is tightly confined loops of oscillating magnetic field that curl around the fictitious arrow of a toroidal dipole vector.