Efficient Excitation of a Toroidal Dipole Mode in All-Dielectric Quadrumer Clusters

We demonstrate a novel design of all-dielectric metasurfaces featuring strong axial toroidal response. A unit cell of the metamaterial is constructed by arranging two types of dielectric disks into an asymmetric quadrumer cluster. The toroidal response is achieved via the excitation of a trapped mode due to the symmetry breaking in the cluster. Dependence of the toroidal response on the degree of asymmetry in the cluster geometry, that appears from the different compositions of holes introduced into the disks, is studied both numerically and experimentally in the microwave regime.