Electrical spin polarization through spin–momentum locking in topological-insulator nanostructures**Project supported by the National Key Basic Research Program of China (Grant Nos. 2014CB921103 and 2017YFA0206304), the National Natural Science Foundation of China (Grant Nos. 61822403, 11874203, U1732159, and U1732273), Fundamental Research Funds for the Central Universities, China (Grant No. 021014380080), and Collaborative Innovation Center of Solid-State Lighting and Energy-Saving Electronics, China.

Abstract

Recently, spin–momentum-locked topological surface states (SSs) have attracted significant attention in spintronics. Owing to spin–momentum locking, the direction of the spin is locked at right angles with respect to the carrier momentum. In this paper, we briefly review the exotic transport properties induced by topological SSs in topological-insulator (TI) nanostructures, which have larger surface-to-volume ratios than those of bulk TI materials. We discuss the electrical spin generation in TIs and its effect on the transport properties. A current flow can generate a pure in-plane spin polarization on the surface, leading to a current-direction-dependent magnetoresistance in spin valve devices based on TI nanostructures. A relative momentum shift of two coupled topological SSs also generates net spin polarization and induces an in-plane anisotropic negative magnetoresistance. Therefore, the spin–momentum locking can enable the broad tuning of the spin transport properties of topological devices for spintronic applications.