拓扑表面态渗流引起的自旋矩和持续电流
Spin torque and persistent currents caused by percolation of topological surface states
摘要：
拓扑绝缘体/铁磁金属（TI/FMM）双层薄膜是一种基于拓扑表面态的自旋电子学器件，其电流诱导自旋力矩效率最高。使用立方晶格模型，我们揭示了表面状态的狄拉克锥的TI可以逐渐合并到或高度交织的FMM体带，和表面状态渗透到FMM，并最终与量子阱态杂交在其中。磁化可以扭曲表面态的自旋-动量锁定，并产生不对称的能带结构，这导致室温持续充电电流的层流。此外，接近FMM也促进了持续的层流自旋电流。通过线性响应理论，我们阐述了表面态和FMM体带有助于电流诱导的自旋力矩，和他们的实波函数呈现的自旋力矩主要是类场的，与表面态的渗透程度的影响很大的幅度。另一方面，杂质可以改变Edelstein效应所预期的自旋极化，并产生类似阻尼的扭矩，并且即使当磁化指向面内并与电流方向正交时也会产生扭矩。
英文摘要：
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.
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