Enhanced group velocity in metamaterials
  The Bruggeman formalism is implemented to estimate the refractive index of an isotropic, dielectric, homogenized composite medium (HCM). Invoking the well--known Hashin--Shtrikman bounds, we demonstrate that the group velocity in certain HCMs can exceed the group velocities in their component materials. Such HCMs should therefore be considered as metamaterials. 
T.G. Mackay (1) and A. Lakhtakia (2) ((1) University of Edinburgh, (2)   Pennsylvania State University)