  Parallel electric and magnetic fields applied to Weyl semimetals pump axial
charge via the axial anomaly until balanced by intervalley relaxation. The
resulting nonequilibrium steady state exhibits the chiral magnetic effect as
well as the anomalous Hall effect, which coupled with Maxwell's equations leads
to unstable electromagnetic waves at low frequency and long wavelength. Here,
we show that such chiral magnetic instability manifests itself as anomalous
reflectance of the surface of pumped Weyl semimetal. Depending on electric,
chiral magnetic, and anomalous Hall conductivities, the reflectance is found to
exceed unity in a finite range of frequency for a circularly polarized light
incident along the direction of Weyl node separation.

Mesoscale and Nanoscale Physics;Optics