Spin-momentum locking and ultrafast spin-charge conversion in ultrathin epitaxial Bi1-xSbx topological insulator

We combine spin- and angle-resolved photo-emission spectroscopy, and time-resolved THz emission spectroscopy to evidence that spin-charge conversion arises mainly from the surface state in Bi1-xSbx ultrathin films, down to few nanometers where confinement effects emerge. We correlate this large conversion efficiency, typically at the level of the bulk spin Hall effect from heavy metals, to the complex Fermi surface obtained from theoretical calculations of the inverse Rashba-Edelstein response. Both surface state robustness and sizeable conversion efficiency in epitaxial Bi1-xSbx thin films bring new perspectives for ultra-low power magnetic random-access memories and broadband THz generation.