All-Dielectric Resonant Metasurfaces with a Strong Toroidal Response

We demonstrate how to design all-dielectric metasurfaces with a strong axial toroidal response by arranging two types of nanodisks into asymmetric quadrumer clusters. This toroidal response is related to the existence of the trapped (dark) mode that appears due to a symmetry breaking in the cluster. We uncover a correlation between the existence of the toroidal response and asymmetry in the metasurface geometries, which originates from different diameters of nanodisks or notches introduced into nanodisks. Because of the unique field configuration of the toroidal mode, the proposed metasurface could serve as a platform for efficient light–matter interaction for enhanced absorption, nonlinear response, and sensing.