From Positive- to Negative-Index Materials: Transitional Phenomena
  Electromagnetic field propagation through a transition layer between the positive-index and negative-index materials with linearly changing dielectric permittivity and magnetic permeability was investigated. It is shown that at oblique incidence, the components of both TE- and TM-waves exhibit singular behavior in the vicinity of the point where both dielectric permittivity and magnetic permeability are equal to zero. In this case, finite dissipation of electromagnetic field energy takes place even at infinitesimally small values of losses. These results are applicable to a broader class of inhomogeneous metamaterials and may provide a new platform for the realization of low intensity nonlinear optics in metamaterials. 
Natalia M. Litchinitser, Andrei I. Maimistov, Ildar R. Gabitov, Roald   Z. Sagdeev, Vladimir M. Shalaev