不同方向局域交换场对锡烯自旋输运的影响

Effects of local exchange field in different directions on spin transport of stanene

利用非平衡格林函数方法,理论研究了多种组合形式的局域交换场对锡烯纳米带自旋输运性质的影响.研究表明锡烯自旋相关电导、边缘态和体能带都显著地依赖于不同区域交换场的方向和强度.在[Ⅰ:±Y,Ⅱ:+Z,Ⅲ:±Y]方向交换场的共同作用下,边缘态受Y方向交换场影响形成带隙,禁带宽度与交换场强度M成正比,在-M <E<M能量范围电导值为0.对上下边缘区域同时施加+Z或-Z方向的交换场时,边缘态和体能带都发生较强的自旋劈裂,自旋向上和向下能带沿相反方向向高能量区域移动,增大交换场的强度电导自旋极化的范围将从高能量扩展到低能量区域.当交换场方向为[Ⅰ:±Z,Ⅱ:±Y,Ⅲ:±Z]时,低能区自旋相关的电导保持电子空穴对称性,不同交换场强度条件下,自旋相关电导都在相同的能量范围-λ<E<λ保持电导平台G_(σ)=e^(2)/h.

Topological insulator is a new quantum state of matter in which spin-orbit coupling gives rise to topologically protected gapless edge or surface states.The nondissipation transport properties of the edge or surface state make the topological device a promising candidate for ultra-low-power consumption electronics.Stanene is a type of two-dimensional topological insulator consisting of Sn atoms arranged similarly to graphene and silicene in a hexagonal structure.In this paper,the effects of various combinations of local exchange fields on the spin transport of stanene nanoribbons are studied theoretically by using the non-equilibrium Green's function method.The results show that the spin-dependent conductance,edge states,and bulk bands of stanene are significantly dependent on the direction and strength of the exchange field in different regions.Under the joint action of the exchange fields in[Ⅰ:土Y,Ⅱ:+Z,Ⅲ:土Y]direction,the edge states form a band-gap under the influence of the Y-direction exchange field.The band-gap width is directly proportional to the exchange field strength M,and the conductance is zero in an energy range of-M<E<M.When the ecohange 5eldo in the direction of+Z or-Z are npplied,ropectively,the upper edge region and the lower edge egion nt the anme time,the opin-up energy band and the opin-down energy band move to in high energy region in oppomite directiong,and otrong opin splitting ooum in the adge otate and bulk bando.Ineresing the ctrength of the ecohango feld,the rnge of opin polsrisntion of conduotnnoe spceada from the high enerev region to the low energy region.When the direotions of the exchnnge feld are[Ⅰ:±Y,Ⅱ:+Z,Ⅲ:±Y],the edge thnteso ae opin degenecate,but the weak opin oplitting oouro in the bulk bando.Under the oondition of different exchange feld strengtho,the opin-dependent oonduotance mnintaino a oonductnnce plntform of G_(σ)=e^(2)/h in the anme eonergy rngoof-λ_(50)<E<λ_(so).