Magnetic field induced valley polarization in a Weyl semimetal with tilted cones.*

We present a theory of the optical conductivity in time-reversal symmetric Weyl semimetals with tilted cones placed under strong magnetic fields. Our theory incorporates long range Coulomb interactions treated within the generalized random phase approximation.
Under irradiation by circularly polarized light, we predict a 100% valley polarization for significant intervals of the incident photon frequency. This polarization, which occurs between nodes related by time-reversal, originates from interband transitions involving the chiral Landau level. We propose observable signatures of this polarization in the optical conductivity and comment on its manifestation in TaAs and related materials.