Negative refraction in Al:ZnO/ZnO metamaterial in the near-infrared
  Noble metals such as gold and silver are the primary metallic building blocks of metamaterial devices. Making subwavelength-sized structural elements from these metals seriously limits the optical performance of a device, however, and complicates the manufacturing process of nearly all metamaterial devices in the optical wavelength range. As an alternative to noble metals, we propose to use heavily-doped oxide semiconductors that offer both functional and fabrication advantages in the near-infrared. In this letter, we report an experimental demonstration of negative refraction in a near-infrared metamaterial device that is designed and fabricated using aluminum-doped zinc oxide. 
Gururaj V. Naik, Jingjing Liu, Alexander V. Kildishev, Vladimir M.   Shalaev and Alexandra Boltasseva
physics.optics cond-mat.mtrl-sci