Thin films of topological Kondo insulator candidate SmB 6 : Strong spin-orbit torque without exclusive surface conduction

The advent of topological insulators (TIs), a novel class of materials that harbor a metallic spin-chiral surface state coexisting with band-insulating bulk, opens up new possibilities for spintronics. One promising route is current-induced switching of an adjacent magnetic layer via spin-orbit torque (SOT), arising from the large spin-orbit coupling intrinsically possessed by TIs. The Kondo insulator SmB has been recently proposed to be a strongly correlated TI, supported by the observation of a metallic surface state in bulk SmB, as evidenced by the thickness independence of the low-temperature resistance plateau. We report the synthesis of epitaxial (001) SmB/Si thin films and a systematic thickness-dependent electrical transport study. Although the low-temperature resistance plateau is observed for all films from 50 to 500 nm in thickness, the resistance is distinctively thickness-dependent and does not support the notion of surface conduction and interior insulation. On the other hand, we demonstrate that SmB can generate a large SOT to switch an adjacent ferromagnetic layer, even at room temperature. The effective SOT generated from SmB is comparable to that from β-W, one of the strongest SOT materials.