A theory of light absorption and circular photocurrent in Weyl semimetals is developed for arbitrary large light intensities with account for both the elastic and inelastic relaxation processes of Weyl fermions. The direct optical transition rate is shown to saturate at large intensity, and the saturation behavior depends on the light polarization and on the ratio of the elastic and inelastic relaxation times. The linear‐circular dichroism in absorption is shown to exceed 10% at intermediate light wave amplitudes and fast energy relaxation. At large intensity I, the light absorption coefficient drops as 1/I, and the circular photogalvanic current increases as I.

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We have studied theoretically the Weyl semimetals the point symmetry group of which has reflection planes and which contain equivalent valleys with opposite chiralities. These include the most frequently studied compounds, namely the transition metals monopnictides TaAs, NbAs, TaP, NbP, and also Bi1−xSbx alloys. The circular photogalvanic current, which inverts its direction under reversal of the light circular polarization, has been calculated for the light absorption under direct optical transitions near the Weyl points. In the studied materials, the total contribution of all the valleys to the photocurrent is nonzero only beyond the simple Weyl model, namely, if the effective electron Hamiltonian is extended to contain either an anisotropic spin-dependent linear contribution together with a spin-independent tilt or a spin-dependent contribution cubic in the electron wave vector k. With allowance for the tilt of the energy dispersion cone in a Weyl semimetal of the C4v symmetry, the photogalvanic current is expressed in terms of the components of the secondrank symmetric tensor that determines the energy spectrum of the carriers near the Weyl node; at low temperature, this contribution to the photocurrent is generated within a certain limited frequency range ∆. The photocurrent due to the cubic corrections, in the optical absorption region, is proportional to the light frequency squared and generated both inside and outside the ∆ window.

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