  We consider the AdS$_4$ RN black hole and work out the momentum dependent
hydrodynamic analysis for the vector modes. We also perform the spectral
function calculation of the dual field theory. As an application, we consider
the permittivity and permeability and find that for low frequency regime, the
index of refraction is found to be negative, supporting the claim made in
ref.\cite{amariti} for AdS$_5$. We also find that at static limit the medium
has the zero permeability, a character of the superconductivity .
