标题： 自旋转移扭矩和拓扑绝缘体/铁磁体垂直异质结构中的自旋极化 显示英文标题

标题： Spin-transfer torque and spin-polarization in topological-insulator/ferromagnet vertical heterostructures

摘要： 我们预测在N/TI/F垂直异质结构中，自由铁磁(F)层的磁化上作用着一种非常规的自旋转移力矩(STT)，这种力矩来源于三维拓扑绝缘体(TI)表面的强自旋-轨道耦合(SOC)，以及当电流从正常金属(N)流过TI薄片体时，电荷电流在传输方向上被自旋极化的现象。 与对称F'/I/F磁性隧道结中的常规STT不同，在线性响应中只有面内STT分量非零，而在N/TI/F结中，面内和垂直力矩都是显著的，且不需要固定F'层作为自旋极化器，这对于自旋电子学应用是有利的。 使用快速传导电子与慢速磁化之间相互作用的非平衡Born-Oppenheimer处理方法，我们推导出一个基于Keldysh格林函数的通用STT公式，这使得在自由F层体内或界面存在SOC的情况下分析力矩成为可能。 显示英文摘要

摘要： We predict an unconventional spin-transfer torque (STT) acting on the magnetization of a free ferromagnetic (F) layer within N/TI/F vertical heterostructures which originates from strong spin-orbit coupling (SOC) on the surface of a three-dimensional topological insulator (TI), as well as from charge current becoming spin-polarized in the direction of transport as it flows from the normal metal (N) across the bulk of the TI slab. Unlike conventional STT in symmetric F'/I/F magnetic tunnel junctions, where only the in-plane STT component is non-zero in the linear response, both the in-plane and perpendicular torque are sizable in N/TI/F junctions while not requiring fixed F' layer as spin-polarizer which is advantageous for spintronic applications. Using the nonequilibrium Born-Oppenheimer treatment of interaction between fast conduction electrons and slow magnetization, we derive a general Keldysh Green function-based STT formula which makes it possible to analyze torque in the presence of SOC either in the bulk or at the interface of the free F layer.