Electrically and Magnetically Resonant dc SQUID Metamaterials
  We propose a superconducting metamaterial design consisting of meta-atoms (MAs) which are each composed of a direct current (dc) superconducting quantum interference device (SQUID) and a superconducting rod. This design provides negative refraction index behavior for a wide range of structure parameters. 
O.V. Shramkova, N. Lazarides, G.P. Tsironis, and A.V. Ustinov
cond-mat.mes-hall cond-mat.supr-con