Optical toroidal dipolar response by an asymmetric double-bar   metamaterial
  We demonstrate that the toroidal dipolar response can be realized in the optical regime by designing a feasible nanostructured metamaterial, comprising asymmetric double-bar magnetic resonators assembled into a toroid-like configuration. It is confirmed numerically that an optical toroidal dipolar moment dominates over other moments. This response is characterized by a strong confinement of an E-field component at the toroid center, oriented perpendicular to the H-vortex plane. The resonance-enhanced optical toroidal response can provide an experimental avenue for various interesting optical phenomena associated with the elusive toroidal moment. 
Zheng-Gao Dong, J. Zhu, Junsuk Rho, Jia-Qi Li, Changgui Lu, Xiaobo   Yin, and X. Zhang
physics.optics