Exceptional Spin-to-Charge Conversion in Selective Band Topology of Bi/Bi_1-xSb_x with Spintronic Singularity

In this study, spin-to-charge conversion (SCC) of various topological materials with ferromagnet is investigated using spintronic terahertz (THz) emission spectroscopy. Compared with other topological materials, significantly large THz emission is observed for topologically nontrivial phases of Bi1-xSbx (x > 0.2) that predominantly originates from the topological surface state. When Bi is superposed above a certain stoichiometry of Bi1-xSbx, it plays a crucial role in generating a highly spin-split state and enhancing the spin-mixing conductance, resulting in colossal THz emission. This proves that improving the SCC efficiency through interface engineering is a useful strategy to design a powerful spintronic device. Collectively, this study proposes a methodology for systematically analyzing SCC efficiency or spin Hall angle using THz emission spectroscopy and offers an efficient structure for future spintronic devices.