Intrinsic spin transport in a topological insulator thin film

Abstract

Topological insulators (TIs) are intriguing materials for advanced computing applications based on spintronics because they can host robust spin effects. For instance, TIs have intrinsically large spin generation enabled by their large spin–orbit coupling. Furthermore, topological surface states (TSS) with spin-momentum locking and Dirac dispersion lead to long spin diffusion. Future spintronic device technology will require scalable film growth of high-quality material. We grow epitaxial films of (Bi1−xSbx)2Te3−ySey (BSTS, x = 0.58, y = 1) and confirm the gapless band structure with optimal doping using angle-resolved photoemission spectroscopy. The temperature dependence of the longitudinal resistivity shows that bulk transport is suppressed as the temperature is decreased, and at low temperature, surface transport dominates. We evaluate the spin transport properties in BSTS without using ferromagnetic tunnel contacts via a non-local resistance experiment as a function of temperature and applied charge current. As expected, these experiments reveal the necessity of decreasing the bulk conduction to best enhance the spin transport. In the TSS, we find a charge-to-spin conversion efficiency (spin Hall angle, θSH∼1) and spin diffusion over several micrometers. Further development of high-quality TIs will make them viable candidates for efficient and lossless spintronics.