Directional Toroidal Dipoles Driven by Oblique Poloidal and Loop Current Flows in Plasmonic Meta-Atoms

Abstract

The toroidal dipole is an exquisite and untraditional electromagnetic mode, categorizing separately from the well-known conventional multipole group which can be robustly localized and squeezed in an extremely tiny spot. In optical subwavelength systems, such a dynamic mode, which can be particularly distinguished as a nonradiating charge-current configuration, manifests in a head-to-tail fashion. Here, going beyond conventional toroidal dipoles, we explained the possibility of the excitation of directional toroidal dipoles in plasmonic meta-atoms driven by controlling the oblique magnetic field and poloidal fluxes. This was done by utilizing an antisymmetric multipixel unit cell with strong toroidal response across the near-infrared band. We showed that the unique structural properties of the proposed asymmetric nanostructure lead to the formation of multiple directional toroidal modes with opposite oblique magnetic fields and reverse poloidal current flows. We envision that this understanding paves nove...