Spin torque and persistent currents caused by percolation of topological surface states

Abstract

The topological insulator/ferromagnetic metal (TI/FMM) bilayer thin films emerged as promising topological surface state-based spintronic devices, most notably in their efficiency of current-induced spin torque. Using a cubic lattice model, we reveal that the surface state Dirac cone of the TI can gradually merge into or be highly intertwined with the FMM bulk bands, and the surface states percolate into the FMM and eventually hybridize with the quantum well states therein. The magnetization can distort the spin-momentum locking of the surface states and yield an asymmetric band structure, which causes a laminar flow of room temperature persistent charge current. Moreover, the proximity to the FMM also promotes a persistent laminar spin current. Through a linear response theory, we elaborate that both the surface state and the FMM bulk bands contribute to the current-induced spin torque, and their real wave functions render the spin torque predominantly field-like, with a magnitude highly influenced by the degree of the percolation of the surface states. On the other hand, impurities can change the spin polarization expected from the Edelstein effect and generate a damping-like torque, and produce a torque even when the magnetization points in-plane and orthogonal to the current direction.

11 pages, 6 figures

References in corpus (5)

• Emergent quantum confinement at topological insulator surfaces
• Surface state dominated spin-charge current conversion in topological insulator/ferromagnetic insulator heterostructures
• Spin-transfer torque and spin-polarization in topological-insulator/ferromagnet vertical heterostructures
• Dirac-Surface-State-Dominated Spin to Charge Current Conversion in the Topological Insulator $(B{i}_{0.22}S{b}_{0.78}{)}_{2}T{e}_3$ Films at Room Temperature
• Theory of Resistivity Upturns in Metallic Cuprates

Cited by in corpus (4)

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• Proximity-induced zero-energy states indistinguishable from topological edge states
• Interface controlled Berry phase and anisotropic spin-charge conversion in altermagnet-topological insulator bilayers
• Magnetoelectric torque and edge currents in spin-orbit coupled graphene nanoribbons