Bi$_2$Se$_3$/EuS界面中的各向异性平面霍尔效应：解析邻近诱导自旋倾斜与拓扑自旋织构的作用
Anisotropic planar Hall effects in Bi$_2$Se$_3$/EuS interfaces: Deciphering the role of proximity induced spin canting and topological spin texture
AI总结：
该研究理论分析Bi$_2$Se$_3$/EuS界面的各向异性平面霍尔与拓扑霍尔效应，揭示Eu矩倾斜、Berry曲率及skyrmion晶体对拓扑表面态输运的影响。
摘要：
铁磁绝缘体EuS与拓扑绝缘体Bi$_2$Se$_3$的邻近耦合已被提出可在Bi$_2$Se$_3$表面附近破缺时间反演对称性，从而在表面Dirac锥中引入能隙或倾斜。作为一种反邻近效应，拓扑表面态中可用的强自旋—轨道耦合能够将EuS铁磁性的Curie温度大幅提高至远超其体相值，并产生磁各向异性。这可导致Eu离子磁矩在垂直于界面的平面内发生倾斜。本文在平面霍尔几何构型下从理论上研究Bi$_2$Se$_3$/EuS界面产生的电子输运性质。基于真实的模型Hamilton量以及Boltzmann输运方程的半经典形式，分析揭示了各向异性平面霍尔电导的若干独特而有趣的特征，其取决于Eu矩倾斜的不同情形：固定的Eu矩倾斜，以及响应外部面内磁场而可自由取向的Eu矩。平面霍尔电导中的各向异性源于带隙拓扑表面态的非对称Berry曲率。我们还探究了Dirac表面态与skyrmion晶体耦合时的拓扑霍尔效应；由于铁磁Heisenberg交换、界面Dzyaloshinskii–Moriya相互作用以及Eu矩垂直排列之间的相互作用，这种skyrmion晶体可在EuS中出现。本研究为通过各向异性平面霍尔效应探测磁交换相互作用与拓扑表面态之间的复杂相互作用提供了新的推动力。
英文摘要：
Proximity coupling of ferromagnetic insulator EuS to the topological insulator Bi$_2$Se$_3$ has been proposed to break time-reversal symmetry near the surface of Bi$_2$Se$_3$, introducing an energy gap or a tilt in the surface Dirac cone. As an inverse proximity effect, strong spin-orbit coupling available in the topological surface states can enhance the Curie temperature of ferromagnetism in EuS largely beyond its bulk value, and also generate a magnetic anisotropy. This can result in a canting of the magnetic moment of Eu ions in a plane perpendicular to the interface. Here, we investigate theoretically electronic transport properties arising from the Bi$_2$Se$_3$/EuS interfaces in the planar Hall geometry. Our analysis, based on a realistic model Hamiltonian and a semi-classical formalism for the Boltzmann transport equation, reveals distinct intriguing features of anisotropic planar Hall conductivity, depending on different scenarios for the canting of the Eu moments: fixed Eu moment canting, and freely-orientable Eu moment in response to the external in-plane magnetic field. The anisotropy in the planar Hall conductivity arises from the asymmetric Berry curvature of the gapped topological surface states. We also explore topological Hall effect of the Dirac surface states, coupled to a skyrmion crystal which can emerge in the EuS due to the interplay of ferromagnetic Heisenberg exchange, interfacial Dzyaloshinskii-Moriya interaction, and perpendicular alignment of the Eu moment. Our study provides new impetus for probing complex interplay between magnetic exchange interactions and topological surface states via anisotropic planar Hall effects.
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