Antitoroidic and Toroidic Orders in All-Dielectric Metasurfaces for Optical Near-Field Manipulation

In material science, multiferroics attract significant interest due to their broad functionality originating from the ability to maintain an interaction between the magnetic and electric polarizability of matter (magnetoelectric effect). The lack of natural multiferroics usable at optical frequencies has led to the search for various approaches to synthesize nanostructures behaving as multiferroics. Herein, we propose a design and study optical properties of an all-dielectric metasurface, which resembles the multiferroic behaviors, and simultaneously maintains both toroidic and antitoroidic orders in the dynamical response on the irradiation by a linearly polarized plane wave. The metasurface is composed of trimer clusters of high-index dielectric particles (disks). The conditions of the appearance of the toroidal dipole moment in the trimer are revealed with the use of the multipole decomposition method. A special technique (secondary multipole decomposition method) is applied to find out how the multipole moments of the trimer are related to the separate multipole moments of its constitutive nanodisks. The spectral properties of the metasurface as well as the electromagnetic near-field distribution are obtained from the full-wave numerical simulation. We demonstrate that both toroidic and antitoroidic orders appear due to specific cluster symmetry reducing, where the toroidal dipole exists as a dark mode of the trimer. At the wavelengths of the toroidal dipole mode excitation, the proposed all-dielectric metasurface possesses a high-quality-factor resonant response accompanied by the near-surface confinement of the strong electromagnetic field with its concentration at the nanoscale. These features make our metasurface to be a platform for chemical or biological sensing, organic light-emitting devices, and large-area laser applications.