  We theoretically discuss the possibility of realizing the negative refractive
index in Weyl/Dirac semimetals. We consider the Maxwell equations with the
plasma gap and the chiral magnetic effect. We study the dispersion relations of
electromagnetic waves, and show that the refractive index becomes negative at
frequencies (just) below the plasma frequency. We find that axial anomaly, or
more specifically, negative magnetoresistance (electric current parallel to
magnetic fields) opens a new route to realize the negative refractive index.
Reflection and transmission coefficients are computed in a slab of Weyl/Dirac
semimetals.
