Optically Generated Spin Current in Two-Dimensional Metallic 2H-MX₂ (M = Nb and Ta and X= S and Se): Role of Anisotropic Spin Splitting

Metallic two-dimensional (2D) transition-metal dichalcogenides (TMDs) (MX2, where M = Nb and Ta and X = S and Se) exhibit Ising-type spin–orbit coupling (SOC), acting as an effective Zeeman field. The Ising-type SOC can induce topological properties such as finite spin Berry curvature (SBC) in the whole Brillouin zone (BZ). Here, utilizing density functional theory, we investigate the spin-dependent optical conductivity of metallic TMD monolayers. We observe a peak in the SBC at the center of the BZ, where no Fermi line exists. This peak arises due to the combined effects of SOC and anisotropic spin splitting in the monolayers of NbSe2 and TaSe2. Finally, we demonstrate how this peak value of SBC at the center of the BZ influences the pure spin Hall current in these monolayers under light irradiation. This study holds potential interest for experimental efforts aimed at designing systems to harvest spin currents through light irradiation in metallic 2D TMDs.