A conductive topological insulator with colossal spin Hall effect for ultra-low power spin-orbit-torque switching

Spin-orbit-torque (SOT) switching using the spin Hall effect (SHE) in heavy metals and topological insulators (TIs) has great potential for ultra-low power magnetoresistive random-access memory (MRAM). To be competitive with conventional spin-transfer-torque (STT) switching, a pure spin current source with large spin Hall angle (${\theta}_{SH}$ > 1) and high electrical conductivity (${\sigma} > 10^5 {\Omega}^{-1}m^{-1}$) is required. Here, we demonstrate such a pure spin current source: BiSb thin films with ${\sigma}{\sim}2.5*10^5 {\Omega}^{-1}m^{-1}$, ${\theta}_{SH}{\sim}52$, and spin Hall conductivity ${\sigma}_{SH}{\sim}1.3*10^7 {\hbar}/2e{\Omega}^{-1}m^{-1}$ at room temperature. We show that BiSb thin films can generate a colossal spin-orbit field of 2770 Oe/(MA/cm$^2$) and a critical switching current density as low as 1.5 MA/cm$^2$ in Bi$_{0.9}$Sb$_{0.1}$ / MnGa bi-layers. BiSb is the best candidate for the first industrial application of topological insulators.