Effect of chaos on two-dimensional spin transport

The role of classical dynamics in spin transport is an intriguing problem from the point of view of classical-quantum correspondence, as spin is a purely relativistic quantum mechanical variable with no classical counterpart. Nevertheless, due to spin-orbit coupling (generally referred to as the relativistic interaction of a particle's spin with its motion inside a potential) and because the orbital motion does have a classical correspondence, the nature of the classical dynamics can affect spin. A basic transport structure is quantum dots, whose geometrical shape can be chosen to lead to characteristically distinct classical behaviors ranging from integrable dynamics to chaos. Whether and how classical chaos can affect spin transport and if the effect can be exploited for applications in spintronics are thus issues of both fundamental and practical interest. Here we report results from systematic, full quantum computations of spin transport through quantum dots hosting different types of classical dynamics. Our main finding is that chaos can play orthogonal roles in affecting spin polarization, depending on the relative strength of the spin-orbit coupling. For weak coupling with a characteristic interaction length much larger than the system size, chaos can be beneficial to preserving spin polarization. In the strong coupling regime where the interaction length is smaller than the system dimension, chaos typically destroys spin polarization. We develop a semiclassical theory to understand these phenomena and point out their implications and potential applications in developing spintronic devices.