  We analyze momentum dependent vector modes in the context of gauge theories
dual to R-charged black holes in $D=4$, $5$ and $7$. For a variety of examples,
the master variables are constructed, for which the linearized equations for
the perturbations decouple. These allow for the computation of momentum
dependent correlation functions. Away from the hydrodynamic limit, numerical
analysis using the decoupled equations of motion is used to obtain the
analogues of the Depine-Lakhtakia (DL) index. For specified ranges of
frequencies, a negative index of refraction is seen to occur in all cases.
