磁绝缘体FeSi中Zak相产生的自旋轨道耦合铁磁表面态的出现
Emergence of spin-orbit coupled ferromagnetic surface state derived from Zak phase in a nonmagnetic insulator FeSi
摘要：
手征化合物FeSi是一种窄禁带绝缘体，具有独特的电荷和自旋动力学特性，超越了简单的能带结构。这些不寻常的特征从拓扑学的角度重新引起人们的关注。虽然表面导电的签名表明，根据尺寸依赖的电阻率在大块晶体，它的存在和拓扑性质仍然难以捉摸。通过对FeSi薄膜的二维电导、磁化强度和自旋电子学功能的多重表征，证明了FeSi薄膜表面固有的铁磁金属态及其强的自旋轨道耦合（SOC）特性。终止的共价键轨道构成极性表面状态与动量相关的自旋纹理由于Rashba型自旋分裂，证实了单向磁阻测量和第一性原理计算。由于自旋-动量锁定，非平衡自旋累积导致磁化翻转。这些表面性质与体能带拓扑的Zak相密切相关。我们的研究结果提出了另一条探索基于SOC的自旋操纵的无贵金属材料的路线。
英文摘要：
A chiral compound FeSi is a nonmagnetic narrow-gap insulator, exhibiting peculiar charge and spin dynamics beyond a simple band-structure picture. Those unusual features have been attracting renewed attention from topological aspects. Although a signature of surface conduction was indicated according to size-dependent resistivity in bulk crystals, its existence and topological properties remain elusive. Here we demonstrate an inherent surface ferromagnetic-metal state of FeSi thin films and its strong spin-orbit-coupling (SOC) properties through multiple characterizations of the two-dimensional (2D) conductance, magnetization and spintronic functionality. Terminated covalent-bonding orbitals constitute the polar surface state with momentum-dependent spin textures due to Rashba-type spin splitting, as corroborated by unidirectional magnetoresistance measurements and first-principles calculations. As a consequence of the spin-momentum locking, non-equilibrium spin accumulation causes magnetization switching. These surface properties are closely related to the Zak phase of the bulk band topology. Our findings propose another route to explore noble-metal-free materials for SOC-based spin manipulation.
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