Circular and magnetoinduced photocurrents in Weyl semimetals

We develop a theory of the direct interband and indirect intraband photogalvanic effects in Weyl semimetals belonging to the gyrotropic classes with improper symmetry operations. At zero magnetic field, an excitation of such a material with circularly polarized light leads to a photocurrent whose direction depends on the light helicity. We show that in the semimetals of the C$_{2v}$ symmetry, an allowance for the tilt term in the effective Hamiltonian is enough to prevent cancellation of the photocurrent contributions from the Weyl cones of opposite chiralities. In the case of the C$_{4v}$ symmetry, in addition to the tilt it is necessary to include terms of the second- or third-order in the electron quasi-momentum. For indirect intraband transitions, the helicity-dependent photocurrent generated within each Weyl node takes on a universal value determined by the fundamental constants, the light frequency and electric field. We have complementarily investigated the magneto-gyrotropic photogalvanic effect, i.e. an appearance of a photocurrent under unpolarized excitation in a magnetic field. In quantized magnetic fields, the photocurrent is caused by optical transitions between the one-dimensional magnetic subbands. A value of the photocurrent is particularly high if one of the photocarriers is excited to the chiral subband with the energy below the cyclotron energy.