Darker than black: radiation-absorbing metamaterial
  We show that corrugated surfaces of hyperbolic metamaterials scatter light preferentially inside the media, resulting in a very low reflectance and ultimate dark appearance in the spectral range of hyperbolic dispersion. This phenomenon of fundamental importance, demonstrated experimentally in arrays of silver nanowires grown in alumina membranes, originates from a broad-band singularity in the density of photonic states. It paves the road to a variety of applications ranging from the stealth technology to high-efficiency solar cells and photodetectors. 
E. E. Narimanov, H. Li, Yu. A. Barnakov, T. U. Tumkur, M. A. Noginov
physics.optics cond-mat.mes-hall