  We study generalized holographic s-wave superconductors in four dimensional
R-charged black hole and Lifshitz black hole backgrounds, in the probe limit.
We first establish the superconducting nature of the boundary theories, and
then study their optical properties. Numerical analysis indicates that a
negative Depine-Lakhtakia index may appear at low frequencies in the theory
dual to the R-charged black hole, for certain temperature ranges, for specific
values of the charge parameter. The corresponding cut-off values for these are
numerically established in several cases. Such effects are seen to be absent in
the Lifshitz background where this index is always positive.
