# Circular photocurrent in Weyl semimetals with mirror symmetry

## TL;DR

This paper theoretically investigates the circular photocurrent in Weyl semimetals with mirror symmetry, revealing conditions under which the photocurrent is nonzero and how it depends on material anisotropies and higher-order corrections.

## Contribution

It identifies the specific Hamiltonian extensions necessary for a nonzero photocurrent in mirror-symmetric Weyl semimetals and derives explicit expressions for the photocurrent considering tilt and cubic corrections.

## Key findings

- Photocurrent is nonzero only with certain Hamiltonian extensions.
- The photocurrent depends on the energy spectrum tensor components.
- Cubic corrections induce frequency-squared dependent photocurrent.

## Abstract

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 Bi$_{1-x}$Sb$_x$ 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 $\bf{k}$. With allowance for the tilt of the energy dispersion cone in a Weyl semimetal of the $C_{4v}$ symmetry, the photogalvanic current is expressed in terms of the components of the second-rank 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 $\Delta $. 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 $\Delta$ window.