Enhancing the Spin Hall Angle in Bi₂Se₃ through Bi Layer Incorporation: A First-Principles Investigation

Previous experimental studies have reported Spin Hall Angle (SHA) values in Bi₂Se₃ films ranging from 2 to 3.5, which exceed theoretical predictions of around 0.26, indicating unexplained mechanisms at play. In this work, we address this discrepancy by introducing Bi bilayers between the quintuple layers of Bi₂Se₃, creating a van der Waals superlattice. Using first-principles calculations, we demonstrate that incorporating Bi layers enhances the spin Hall conductivity (SHC) by more than sixfold, while reducing electrical conductivity (EC) through grain boundary scattering and thickness-dependent effects. The Bi bilayers shift electronic states near the Fermi level, yielding SHC values that approach those of bulk Bi. Additionally, our calculations, which account for electron-phonon scattering and grain size effects, show a significant reduction in EC, further increasing the SHA. These results suggest that the incorporation of Bi layers in Bi₂Se₃ can enhance spin transport properties, providing a promising pathway for the development of more efficient spintronic devices.