Enhancement of Magneto-Chiral Effect in Photonic Crystals

We theoretically study a magneto-chiral effect magnified in photonic crystals. A magneto-chiral effect is a directional birefringence even for unpolarized light. This effect occurs in a material such as GaFeO$_3$ in which both time-reversal and inversion symmetries are broken. Unfortunately the wave vector dependence of a dielectric function is typically the order of $10^{-4}$, which is too small to observe. We consider one-dimensional photonic crystals composed of the magneto-chiral medium and air, and calculate the reflectivity. We found that the difference in the reflectivities with respect to different magnetization configurations is thousands of times enhanced compared with that in a bulk material.