A negative permeability material at red light
  Experimental demonstration of a negative permeability due to near-field coupling of periodic thin silver strips is presented. Two samples with different strip thicknesses are fabricated; optical measurements of the samples confirm our initial design projections by showing the real part of permeability to be about -1 for the sample with thinner strips and -0.8 for the sample with thicker strips at wavelengths of 770 nm and 720 nm. 
Hsiao-Kuan Yuan, Uday K. Chettiar, Wenshan Cai, Alexander V.   Kildishev, Vladimir P. Drachev, Alexandra Boltasseva, and Vla...