Light-assisted Néel spin currents in $\mathrm{PT}$-symmetric antiferromagnetic semiconductors

Néel spin current is defined as the staggered spin current across different magnetic sublattices and can manipulate the Néel vector of the antiferromagnet by its associated spin-transfer torques. Currently, it is believed that Néel spin currents are only generated through electrical driving in $\mathrm{PT}$-symmetric antiferromagnetic metals, which is a linear effect. In this paper, we propose that Néel spin currents can be induced through the nonlinear optical effect (spin photogalvanic effect) in $\mathrm{PT}$-symmetric antiferromagnetic semiconductors. Using CrSBr and ${\mathrm{CrI}}_3$ as representatives, we predict that light can generate Néel spin current in antiferromagnetic semiconductors, with both staggered and antiparallel spin currents distributed across different magnetic sublattices, depending on the $\mathrm{PT}$ symmetries of their corresponding spin photogalvanic coefficients. We show that the origin of the diverse manifestations of light-assisted Néel spin currents lies in the nonlinearity of the spin photogalvanic effect, resulting in the current not necessarily being the staggered spin current. Our work proposes a nonlinear effect that may have tremendous application potential in future antiferromagnetic devices.