Spin Transport Theory Beyond Drift-Diffusion Equation

本理论研究的重点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，其有效性尚未在理论上得到证明。通过引入用图表示半经典玻尔兹曼方程中的项的思想，可以将自旋输运性质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做绝热近似的情况下发展随时间的自旋输运理论。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，提供磁系统的吉尔伯特阻尼机制。在不绝热冻结局部磁化自由度的情况下，用图解法求解玻尔兹曼方程的时间依赖性。本研究的预期成功将增强对各种非均匀体系（包括磁性多层、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准则，并为解释大量实验数据提供一套新的规则。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，导致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通过参与信息存储产业联盟与业界进行互动。这项理论研究研究了不同结构中的磁输运。本研究的预期成功将增强对各种非均匀体系（包括磁性多层、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准则，并为解释大量实验数据提供一套新的规则。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，导致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通过参与信息存储产业联盟（Information Storage industry Consortium）与业界进行互动

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.***