Research Center for Applied Sciences, Academia Sinica , Taipei 11529, Taiwan.
Department of Physics, National Taiwan University , Taipei 10617, Taiwan.
ACS Nano. 2018 Feb 27;12(2):1920-1927. doi: 10.1021/acsnano.7b08828. Epub 2018 Feb 5.
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 nonradiating 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.
环形偶极子是一种与常见的磁偶极子和电偶极子无关的局域电磁激发。它对应于沿着环的小环流动的电流。辐射感应环形偶极子和电偶极子的干涉导致非辐射电荷-电流配置，即磁单极子。感应环形偶极子与电磁波的相互作用最近在微波、太赫兹和光学频率的人工介质中得到了观察。在这里，我们展示了一种准平面等离子体超材料，它由哑铃形孔和垂直分裂环谐振器组成，在正常入射电磁波激发下，在光谱的光学部分表现出横向环形矩和共振磁单极子行为。我们的结果实验证明，环形模式和磁单极子模式可以在传统的透射和反射实验中对物质薄片在光谱光学部分的吸收和色散提供独特且具有物理意义的贡献。
