Negative refractive index in cubic noncentrosymmetric superconductors

We study the negative refractive index in cubic noncentrosymmetric superconductors.We consider the Maxwell equations under the Meissner effect, and the magnetoelectric effect arising due to inversion-symmetry breaking. We derive the dispersion relations of electromagnetic waves and show that the refractive index becomes negative at frequencies just below the plasma gap. We find that the chiral mechanism of the negative refractive index, which is usually discussed in chiral materials with negative permittivity, can be directly applied to noncentrosymmetric superconductors with positive permittivity. A rough estimation from experimental values of the penetration depth of LiPt3B indicates that a negative refractive index may appear in UV regions.