Magneto-optical response of chiral fermions.

Dirac and Weyl materials possess chiral fermions, which are characterized by nontrivial topology and large Berry curvature. Chiral fermions have nontrivial interactions with magnetic fields and light. We propose three different mechanisms for magnetic photocurrents caused by chiral fermions, with different requirements on the symmetry group of the crystal.

In Dirac and Weyl materials, we predict that the chiral anomaly results in generation of chiral charge in response to circularly polarized light. This causes an anomalous photocurrent in the direction of an applied DC magnetic field.

In Weyl materials with a reflection plane, such as TaAs, the tilt of the cones causes an anisotropic interaction with magnetic field, and we predict a photocurrent perpendicular to an external field in response to linearly polarized light.

In materials with chiral crystal structure and multifold fermions, such as CoSi, if the Fermi level is not exactly at the Weyl node, we predict a photocurrent parallel to an external magnetic field, in response to linearly polarized light.