Topological Surface States Originated Spin-Orbit Torques in Bi(2)Se(3)

The three dimensional topological insulator bismuth selenide (Bi(2)Se(3)) is expected to possess strong spin-orbit coupling and spin-textured topological surface states and, thus, exhibit a high charge to spin current conversion efficiency. We evaluate spin-orbit torques in Bi(2)Se(3)/Co(40)Fe(40)B(20) devices at different temperatures by spin torque ferromagnetic resonance measurements. As the temperature decreases, the spin-orbit torque ratio increases from ∼0.047 at 300 K to ∼0.42 below 50 K. Moreover, we observe a significant out-of-plane torque at low temperatures. Detailed analysis indicates that the origin of the observed spin-orbit torques is topological surface states in Bi(2)Se(3). Our results suggest that topological insulators with strong spin-orbit coupling could be promising candidates as highly efficient spin current sources for exploring the next generation of spintronic applications.