Dirac-surface-state-dominated spin to charge current conversion in the topological insulator (Bi[subscript 0.22]Sb[subscript 0.78])[subscript 2]Te[subscript 3] films at room temperature

Abstract

We report the spin-to-charge current conversion in an intrinsic topological insulator (TI) (Bi[subscript 0.22]Sb[subscript 0.78])[subscript 2]Te[subscript 3] film at room temperature. The spin currents are generated in a thin layer of permalloy (Py) by two different processes, the spin pumping effect (SPE) and the spin Seebeck effect (SSE). In the first, we use microwave-driven ferromagnetic resonance of the Py film to generate a SPE spin current that is injected into the TI (Bi[subscript 0.22]Sb[subscript 0.78])[subscript 2]Te[subscript 3] layer in direct contact with Py. In the second, we use the SSE in the longitudinal configuration in Py without contamination by the anomalous Nernst effect, which was made possible with a thin NiO layer between the Py and (Bi[subscript 0.22]Sb[subscript 0.78])[subscript 2]Te[subscript 3] layers. The spin-to-charge current conversion is dominated by the TI surface states and is attributed to the inverse Edelstein effect (IEE), which is made possible by the spin-momentum locking in the electron Fermi contours due to the Rashba field. The measurements by the two techniques yield very similar values for the IEE parameter, which are larger than the reported values in the previous studies on topological insulators.