Effect of surface hybridization on RKKY coupling in ferromagnet/topological insulator/ferromagnet trilayer system
Effect of surface hybridization on RKKY coupling in ferromagnet/topological insulator/ferromagnet trilayer system
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DOI：
10.1063/1.4977072
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发表时间：
2016-11
期刊：
影响因子：
1.6
通讯作者：
Cong Son Ho;M. Jalil
中科院分区：
文献类型：
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作者：
Cong Son Ho;M. Jalil
我们从理论上研究了由拓扑绝缘体薄膜 (TI) 分隔的两个铁磁体 (FM) 之间的 RKKY 交换耦合。我们发现 RKKY 交换耦合 Φex 对 TI 厚度 (tTI) 的不同寻常的依赖性。首先，当 tTI 减小时，耦合幅度首先增大，并在某个临界厚度处达到最大值，低于该值，幅度开始减小。这种趋势归因于TI薄膜表面之间的杂化，其在临界厚度以下打开了间隙，从而将表面从半金属态转变为绝缘态。在绝缘阶段，间隙张开引起的抗磁性补偿了狄拉克态的顺磁性，导致磁化率递减和RKKY耦合。对于典型参数，Bi2Se3 薄膜的临界厚度估计在 3-5 nm 范围内。
We theoretically investigate the RKKY exchange coupling between two ferromagnets (FM) separated by a thin topological insulator film (TI). We find an unusual dependence of the RKKY exchange coupling Φex on the TI thickness (tTI). First, when tTI decreases, the coupling amplitude increases at first and reaches its maximum value at some critical thickness, below which the amplitude turns to diminish. This trend is attributed to the hybridization between surfaces of the TI film, which opens a gap below critical thickness and thus turns the surfaces into insulating state from semi-metal state. In insulating phase, diamagnetism induced by the gap-opening compensates paramagnetism of Dirac state, resulting in a diminishing magnetic susceptibility and RKKY coupling. For typical parameters, the critical thickness in Bi2Se3 thin film is estimated to be in the range of 3-5 nm.