Magnetic Toroidal Dipole and Toroid-Like Modes in Hybrid Plasmonic-Dielectric Resonator

Jun Jun Xiao College of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, China Qiang Zhang College of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, China Dezhuan Han Department of Applied Physics, Chongqing University, Chongqing, China Lei Gao School of Physical Science and Technology, Soochow University, Suzhou, China

Recently the plasmonic or dielectric toroidal moments have gained much attention because that the toroidal responses are usually inconspicuous but can be dramatically enhanced in metamaterials [1]. It has been justified that one of the cavity modes in a circular metal-dielectric-metal resonator (CMDMR) has dominant magnetic toroidal dipole moment. We analytically and numerically show that lateral plasmonic coating can be an interesting way to mediate the cavity modes in the CMDMR. As the lateral plasmonic coating transforms the sandwiched circular resonator to a core-shell nanodisk (CSND), it is shown that all the usual in-plane magnetic modes are eliminated and only toroidal and toroid-like cavity modes can survive in the CSND [e.g., see Fig. 1(a)] [2]. All these modes are resulted from the coherent cylindrical surface plasmon waves with approximately the Dirichlet boundary condition [see Fig. 1(b)]. Moreover, in a rotationally discrete CSND structure, i.e., cage-like split ring resonators (C-SRRs) sharing the gap, it is shown that two of the three lowest order resonance modes in this C-SRR stereomatematerial have strong magnetic toroidal dipole response. All the three resonance modes in the C-SRR are derived from the hybridization of the fundamental and the second-order modes in the corresponding individual SRR [3]. Our results provide a different platform to explore the toroidal dipole and the combination of toroidal moments, may finding application in plasmonic nanoantennas, emission enginenering, and functional metamaterial design.

Fig. 1. (a) Near field pattern of the toroid-like cavity modes in CSND, the upper panels show the out-of-plane electric field and the lower panels show the in-plane magnetic fields. (b) The resonance frequencies (symbols) of the CSND all fall on the dispersion curve (solid line) of gap surface plasmon wave, is the th zero point of the th Bessel function, the radius and the thickness of dielectric layer. Fig. 1. (a) Near field pattern of the toroid-like cavity modes in CSND, the upper panels show the out-of-plane electric field and the lower panels show the in-plane magnetic fields. (b) The resonance frequencies (symbols) of the CSND all fall on the dispersion curve (solid line) of gap surface plasmon wave, is the th zero point of the th Bessel function, the radius and the thickness of dielectric layer.

Fig. 1. (a) Near field pattern of the toroid-like cavity modes in CSND, the upper panels show the out-of-plane electric field and the lower panels show the in-plane magnetic fields. (b) The resonance frequencies (symbols) of the CSND all fall on the dispersion curve (solid line) of gap surface plasmon wave, χmn is the nth zero point of the mth Bessel function, the radius and the thickness of dielectric layer.

References:

[1] Kaelberer, V. A. Fedotov. N. Papasimakis, D. P. Tsai, and N. I. Zheludev, Science 330, 1510 (2010).

[2] Q. Zhang, J. J. Xiao, X. M. Zhang, D. Han, and L. Gao, ACS Photonics, 10.1021/ph500229p (2014).

[3] S. L. Wang, J. J. Xiao, Q. Zhang, and X. M. Zhang, Opt. Express 22, 24358 (2014).

eiexiao@hitsz.edu.cn









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