Room-Temperature Spin-Orbit Torque from Topological Surface States.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Spin-momentum locked surface states in topological insulators (TIs) offer potential for high spin-orbit torque (SOT) efficiency.
• Previous studies show significant discrepancies in reported SOT efficiencies for TIs.
• Heavy metals (HMs) are conventionally used for SOT generation via bulk spin-orbit coupling.

Purpose of the Study:

• To systematically evaluate and compare SOT efficiency in TI/HM systems using a consistent methodology.
• To assess the potential of TIs as superior materials for SOT applications.
• To investigate the influence of the Fermi level position on SOT efficiency in (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$.

Main Methods:

• Fabrication and characterization of TI(HM)/Ti/CoFeB/MgO heterostructures.
• Systematic measurement of SOT efficiency across different TI and HM materials using a unified experimental approach.
• Investigation of SOT efficiency dependence on Fermi level tuning in (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$.

Main Results:

• Topological insulators exhibit SOT efficiency more than an order of magnitude higher than conventional heavy metals at room temperature.
• Achieved a low switching current density of 5.2×10$^{5}$ A cm$^{-2}$ using (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$.
• SOT efficiency in (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$ is significantly enhanced near the Dirac point, correlating with insulating bulk and conducting surface states.

Conclusions:

• Topological insulators offer a pathway to significantly enhance SOT efficiency beyond heavy metals.
• The dominant contribution to SOT in these systems originates from the topological surface states.
• This work confirms the ultrahigh SOT efficiency achievable from topological surface states, paving the way for advanced spintronic devices.