Planar Metamaterial with Toroidal Moment
  We observe toroidal response from a planar metamaterial comprised of asymmetric split ring resonators (ASRRs). It is showed that a toroidal-molecule can be constructed through rational arrangement of planar ASRRs as meta-atoms via manipulating structural symmetry of the meta-atoms. Field maps clearly indicate that the toroidal resonance paves new electromagnetic confinement style in a subwavelength scale. Planar scheme of manipulating the coupling among the ASRRs may stimulate research in optical region involving toroidal multipoles. Toroidal geometry together with the Fano resonance made high-Q response will have enormous potential applications in low-threshold lasing, cavity quantum electrodynamics and nonlinear processing. 
Yuancheng Fan, Zeyong Wei, Hongqiang Li, Hong Chen, Costas M.   Soukoulis
physics.optics cond-mat.mtrl-sci