Spin Transport Theory Beyond Drift-Diffusion Equation

本文的主要工作是在不使用漂移扩散方程的情况下推广自旋输运理论，并研究非绝热过程对自旋输运的影响。 最近发现了许多新的自旋相关现象，但对这些现象的理解主要是基于简单的宏观方程，如漂移扩散自旋方程，其有效性尚未得到理论证明。 通过引入将半经典玻尔兹曼方程中的项用图表示的思想，自旋输运性质可以扩展到漂移扩散方程之外。 这些图表对于深入了解这些术语所代表的物理过程非常有用。 本研究的另一个重点将是在不作绝热近似的情况下发展含时自旋输运理论。 非平衡载流子和局部磁矩之间的非绝热过程产生摩擦力矩，该摩擦力矩提供磁系统的吉尔伯特阻尼机制。 Boltzmann方程的时间依赖性将通过图解技术求解，而不会冻结局部磁化的自由度。预期这项研究的成功将提高对各种非均匀系统，包括磁性多层膜，半导体异质结构和磁性纳米结构中自旋输运现象的基本理解。 研究结果将为常用的漂移扩散方程提供理论依据，并为解释大量实验数据提供新的规则。 除了为研究生和博士后提供培训外，该项目还将产生广泛的影响，促进密苏里州小组与世界各地的合作者之间的知识交流。 此外，PI还通过参与信息存储行业联盟与行业进行互动。%%本理论研究研究了各种结构中的磁输运。 这项研究的预期成功将加强对各种非均匀系统中自旋输运现象的基本理解，包括磁性多层膜，半导体异质结构和磁性纳米结构。 研究结果将为常用的漂移扩散方程提供理论依据，并为解释大量实验数据提供新的规则。 除了为研究生和博士后提供培训外，该项目还将产生广泛的影响，促进密苏里州小组与世界各地的合作者之间的知识交流。 此外，PI通过参加信息存储行业联盟与行业互动。

The focus of this theoretical research is to generalize spin transport theory without using the drift-diffusion equation and to investigate the effect of non-adiabatic processes of spin transport. Many novel spin-dependent phenomena have recently been discovered, but the understanding of these phenomena is largely based on simple macroscopic equations such as drift-diffusion spin equations whose validity has not been theoretically justified. By introducing the idea of representing the terms in the semiclassical Boltzmann equation in terms of diagrams, spin transport properties can be extended beyond the drift-diffusion equation. These diagrams are extremely useful for providing an insight into physical processes which these terms represent. Another focus of this research will be on the development of the time-dependent spin transport theory without making an adiabatic approximation. Non-adiabatic processes between non-equilibrium carriers and local magnetic moments create a friction torque that provides a Gilbert damping mechanism of magnetic systems. The time-dependence of the Boltzmann equation will be solved by diagrammatic techniques without adiabatically freezing the degree of freedom of the local magnetization.The anticipated success of this research will enhance fundamental understanding of spin transport phenomena in various inhomogeneous systems including magnetic multilayers, semiconductor heterostructure, and magnetic nanostructure. The research results will supply theoretical criteria on those commonly used drift-diffusion equations and provide a new set of rules to interpret vast experimental data. In addition to providing training for graduate students and postdoctoral associates, the project will have a broad impact of resulting in exchanges of knowledge between the Missouri group and collaborators around the world. Also, the PI interacts with industry through his participation in the Information Storage Industry Consortium.%%This theoretical research studies magnetic transport in various structures. The anticipated success of this research will enhance fundamental understanding of spin transport phenomena in various inhomogeneous systems including magnetic multilayers, semiconductor heterostructure, and magnetic nanostructure. The research results will supply theoretical criteria on those commonly used drift-diffusion equations and provide a new set of rules to interpret vast experimental data. In addition to providing training for graduate students and postdoctoral associates, the project will have a broad impact of resulting in exchanges of knowledge between the Missouri group and collaborators around the world. Also, the PI interacts with industry through his participation in the Information Storage Industry Consortium.***