[论文解读] Spin Hall effect

Jairo Sinova, Sergio O. Valenzuela+3 more|arXiv (Cornell University)|Nov 12, 2014

Quantum and electron transport phenomena被引用 7

一句话总结

本文对自旋霍尔效应（SHE）进行了全面综述，解释了如何通过自旋-轨道耦合使电流产生横向自旋流。文章整合了实验与理论进展，将光学、输运及磁化动力学测量与现象学理论及微观理论相联系，并确立了自旋霍尔角和自旋泵浦机制作为量化自旋流的关键工具。

ABSTRACT

Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Although first observed only a decade ago, these effects are already ubiquitous within spintronics as standard spin-current generators and detectors. Here we review the experimental and theoretical results that have established this sub-field of spintronics. We focus on the results that have converged to give us a clear understanding of the phenomena and how they have evolved from a qualitative to a more quantitative measurement of spin-currents and their associated spin-accumulation. Within the experimental framework, we review optical, transport, and magnetization-dynamics based measurements and link them to both phenomenological and microscopic theories of the effect. Within the theoretical framework, we review the basic mechanisms in both the extrinsic and intrinsic regime which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. We also review the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin-generation which has proven important in the measurements of the spin Hall angle. We further connect the spin-current generating spin Hall effect to the inverse spin galvanic effect, which often accompanies the SHE, in which an electrical current induces a non-equilibrium spin polarization. These effects share common microscopic origins and can exhibit similar symmetries when present in ferromagnetic/non-magnetic structures through their induced current-driven spin torques. Although we give a short chronological overview, the main body is structured from a pedagogical point of view, focusing on well-established and accepted physics.

研究动机与目标

• 整合自旋霍尔效应作为自旋电子学核心现象的实验与理论理解。
• 阐明自旋流与自旋积累的测量从定性到定量的转变过程。
• 将自旋霍尔效应与相关现象（如反常霍尔效应和逆自旋塞曼效应）相联系。
• 建立一个教学框架，将微观理论与可测量物理量（如自旋霍尔角）相联系。
• 统一现象学模型（如自旋扩散方程）与自旋泵浦理论，用于自旋流的生成与探测。

提出的方法

• 综述包括自旋流光学、输运及磁化动力学测量在内的实验技术。
• 利用微观理论与现象学理论分析自旋霍尔效应的非本征与本征机制。
• 应用自旋扩散方程描述特定区域（特别是非磁性材料）中的自旋输运。
• 利用自旋泵浦理论建模界面处的自旋流生成，尤其在铁磁/非磁异质结构中。
• 建立自旋霍尔效应与逆自旋塞曼效应之间的对称性与微观联系。
• 将理论框架与实验数据对比，以验证自旋霍尔角与自旋积累的量化结果。

实验结果

研究问题

• RQ1 非磁性材料中自旋霍尔效应的基本微观机制是什么？
• RQ2 自旋霍尔效应的非本征与本征贡献有何不同？它们与铁磁体中反常霍尔效应的关系如何？
• RQ3 在何种条件下自旋扩散方程适用于建模自旋霍尔体系中的自旋输运？
• RQ4 自旋泵浦理论如何实现自旋霍尔角的定量测量？
• RQ5 从对称性与微观起源角度，自旋霍尔效应与逆自旋塞曼效应之间存在何种关系？

主要发现

• 自旋霍尔效应现已被广泛确立为自旋电子器件中生成与探测自旋流的可靠机制。
• 通过自旋泵浦与基于输运的实验技术，自旋流的定量测量已取得显著进展。
• 自旋霍尔角已被实验验证为连接电流传导与自旋流生成的关键参数。
• 包括自旋扩散与自旋泵浦模型在内的理论框架，成功描述了非磁性体系中的自旋输运与生成行为。
• 自旋霍尔效应与逆自旋塞曼效应具有共同的微观起源，并在铁磁/非磁异质结构中表现出相似的对称性。
• 自旋霍尔效应与反常霍尔效应之间的联系，为非磁性与磁性材料中自旋-轨道耦合现象提供了统一的理解。