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. ***
