  The Rashba interaction induced when inversion symmetry is broken in solids is
a key interaction connecting spin and charge for realizing novel
magnetoelectric cross-correlation effects. Here, we theoretically explore the
optical properties of a bulk Rashba conductor by calculating the transport
coefficients at finite frequencies. It is demonstrated that the combination of
direct and inverse Edelstein effects leads to a softening of the plasma
frequency for the electric field perpendicular to the Rashba field, resulting
in a hyperbolic electromagnetic metamaterial. In the presence of magnetization,
a significant enhancement of anisotropic propagation (directional dichroism) is
predicted because of interband transition edge singularity.Based on an
effective Hamiltonian analysis, the dichroism is demonstrated to be driven by
toroidal and quadratic moments of the magnetic Rashba system. The effective
theory of the cross-correlation effects has the same mathematical structure as
that of insulating multiferroics.
