Ho Cong Son, Wang Yi, Siu Zhou Bin, Tan Seng Ghee, Jalil Mansoor B A, Yang Hyunsoo
Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, 117576, Singapore.
Data Storage Institute, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, 08-01, Innovis, Singapore.
Sci Rep. 2017 Apr 11;7(1):792. doi: 10.1038/s41598-017-00911-4.
We investigate the thickness optimization for maximum current-induced spin-orbit torque (SOT) generated by topological surface states (TSS's) in a bilayer system comprising of a ferromagnetic layer coupled to a thin topological insulator (TI) film. We show that by reducing the TI thickness, two competing effects on the SOT are induced: (i) the torque strength is stronger as the bulk contribution is decreased; (ii) on the other hand, the torque strength becomes suppressed due to increasing hybridization of the surface states. The latter is attributed to the opposite helicities of the coupled TSS's. We theoretically model the interplay of these two effects and derive the optimal TI thickness to maximize the spin torque, which is estimated to be about 3-5 nm for typical BiSe films.
我们研究了在由与薄拓扑绝缘体（TI）薄膜耦合的铁磁层组成的双层系统中，为使拓扑表面态（TSS）产生的最大电流诱导自旋轨道矩（SOT）实现厚度优化的问题。我们表明，通过减小TI厚度，会对SOT产生两种相互竞争的效应：（i）随着体贡献的减小，转矩强度更强；（ii）另一方面，由于表面态的杂化增加，转矩强度受到抑制。后者归因于耦合TSS的相反螺旋度。我们从理论上对这两种效应的相互作用进行建模，并推导出使自旋转矩最大化的最佳TI厚度，对于典型的BiSe薄膜，该厚度估计约为3 - 5纳米。
