Spontaneous emission enhancement in metal-dielectric metamaterials
  We study the spontaneous emission of a dipole emitter imbedded into a layered metal-dielectric metamaterial. We demonstrate ultra-high values of the Purcell factor in such structures due to a high density of states with hyperbolic isofrequency surfaces. We reveal that the traditional effective-medium approach greatly underestimates the value of the Purcell factor due to the presence of an effective nonlocality, and we present an analytical model which agrees well with numerical calculations. 
Ivan Iorsh, Alexander Poddubny, Alexey Orlov, Pavel Belov and Yuri   Kivshar
physics.optics cond-mat.mtrl-sci