# Nonlinear Absorption and Photocurrent in Weyl Semimetals

## TL;DR

This paper develops a comprehensive theory for light absorption and photocurrent generation in Weyl semimetals, accounting for nonlinear effects and relaxation processes, revealing saturation behaviors and polarization-dependent phenomena at high intensities.

## Contribution

It introduces a novel theoretical framework for nonlinear optical responses in Weyl semimetals, including saturation effects and polarization dependence, at arbitrary light intensities.

## Key findings

- Optical transition rate saturates at high intensity, influenced by polarization and relaxation times.
- Absorption coefficient decreases as 1/√I at large intensities.
- Circular photocurrent increases as √I with increasing light intensity.

## Abstract

Theory of light absorption and circular photocurrent in Weyl semimetals is developed for arbitrary large light intensities with account for both elastic and inelastic relaxation processes of Weyl fermions. The direct optical transition rate is shown to saturate at large intensity, and the saturation behaviour 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 $1/\sqrt{I}$, and the circular photogalvanic current increases as $\sqrt{I}$.