Efficient charge-spin conversion and magnetization switching through the Rashba effect at topological-insulator/Ag interfaces

We report the observation of efficient charge-to-spin conversion in the three-dimensional topological insulator (TI) Bi2Se3 and Ag bilayer by the spin-torque ferromagnetic resonance technique. The spin-orbit-torque ratio in the Bi2Se3/Ag/CoFeB heterostructure shows a significant enhancement as the Ag thickness increases to similar to 2 nm and reaches a value of 0.5 for 5 nm Ag, which is similar to 3 times higher than that of Bi2Se3/CoFeB at room temperature. The observation reveals the interfacial effect of Bi2Se3/Ag exceeds that of the topological surface states (TSSs) in the Bi2Se3 layer and plays a dominant role in the charge-to-spin conversion in the Bi2Se3/Ag/CoFeB system. Based on first-principles calculations, we attribute our observation to the large Rashba splitting bands which wrap the TSS band and have the same net spin polarization direction as the TSS of Bi2Se3. Subsequently, we demonstrate Rashba-induced magnetization switching in Bi2Se3/Ag/Py with a low current density of 5.8 x 10(5) A/cm(2).