Monolayer ${\mathrm{NbSe}}_2$ is a metallic two-dimensional (2D) transition-metal dichalcogenide material. Owing to the lattice structure and the strong atomic spin-orbit coupling (SOC) field, monolayer ${\mathrm{NbSe}}_2$ possesses Ising-type SOC which acts as an effective Zeeman field, leading to the unconventional topological spin properties. In this paper, we numerically calculate spin-dependent optical conductivity of monolayer ${\mathrm{NbSe}}_2$ using Kubo formula based on an effective tight-binding model which includes $d_{z^2}, d_{x^2-y^2}$, and $d_{xy}$ orbitals of Nb atoms. Numerical calculation indicates that the up- and down-spin have opposite sign of Hall current, so the pure spin Hall current can be generated in monolayer ${\mathrm{NbSe}}_2$ under light irradiation, owing to the topological nature of monolayer ${\mathrm{NbSe}}_2$, i.e., finite spin Berry curvature. The spin Hall angle is also evaluated. The optically induced spin Hall current can be enhanced by the electron doping and persists even at room temperature. Our results will serve to design opt-spintronics devices such as spin current harvesting by light irradiation on the basis of 2D materials.

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• Optical conductivity
• Spin-orbit coupling
• Topological materials
• Topological phases of matter
• 2-dimensional systems
• Graphene
• Honeycomb lattice
• Transition metal dichalcogenides
• Two-dimensional electron system
• Tight-binding model