Tuning toroidal dipole resonances in dielectric metamolecules by an additional electric dipolar response

Abstract

With the rise of artificial magnetism and metamaterials, the toroidal family recently attracted more attention for its unique properties. Here, we propose an all-dielectric pentamer metamolecule consisting of nano-cylinders with two toroidal dipolar resonances, whose frequencies, EM distributions, and Q factor can be efficiently tuned due to the additional electric dipole mode offered by a central cylinder. To further reveal the underlying coupling effects and the formation mechanism of toroidal responses, the multiple scattering theory is adopted. It is found that the first toroidal dipole mode, which can be tuned from 2.21 to 3.55μm, is mainly induced by a collective electric dipolar resonance, while the second one, which can be tuned from 1.53 to 1.84μm, relies on the cross coupling of both electric and magnetic dipolar responses. The proposed low-loss metamolecule and mode coupling analyses may pave the way for the efficient design of toroidal responses in advanced optical devices.