Giant spin-to-charge conversion by tailoring magnetically proximitized topological Dirac semimetal

While ferromagnet and topological material bilayers are widely studied to obtain efficient spin charge conversion via topological surface states (TSS), the influence of the magnetic proximity effect (MPE) on the TSS evolution and conversion efficiency remains poorly understood. In this study, we experimentally probe and reveal the behavior of spin momentum locked TSS through spin pumping measurements in heterostructures composed of ferromagnetic Fe and the topological Dirac semimetal alpha Sn. As the alpha Sn thickness (tSn) increases from 9 to 35 nm, the Gilbert damping constant of the Fe layer exhibits a pronounced peak at tSn = 25 nm, followed by a decrease at greater thicknesses. Our rigorous theoretical analysis, combining analytical modeling and first principles calculations, attributes this behavior to the TSS disappearance at the Fe and alpha Sn interface and exchange gap opening on the opposite surface, both induced by the long range MPE and its influence on the spin charge conversion efficiency. At tSn = 25 nm, we demonstrate highly efficient spin charge conversion with an inverse Edelstein length of 3.14 nm, the highest value reported at room temperature for ferromagnet and topological material bilayers. These findings underscore the critical role of tuning TSS properties under MPE for advancing topological materials in spintronic applications.