Effect of chaos on two-dimensional spin transport

Abstract

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 the 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.

A Chirality-Based Quantum Leap

“…20. The idea originates from recent studies to control spin polarization by exploiting classical chaotic dynamics 238,239 and spin Fano resonances. 240 The role of classical dynamics in spin transport is intriguing from the point of view of a classical-quantum correspondence, as spin is a purely relativistic quantum mechanical variable without a classical counterpart.…”

“…Of particular interest is the spin degree of freedom in the weak SO coupling regime where, as existing studies suggested, it is possible to use classical chaos to enhance SO entanglement significantly at the expense of spin coherence. [238][239][240]…”

“…A potential approach is to exploit a hybrid structure that couples a chiral molecule to a 2D QD to form a “super chiral molecule” to control and manipulate spin polarization, as illustrated schematically in Figure . The idea originates from recent studies to control spin polarization by exploiting classical chaotic dynamics , and spin Fano resonances …”

“…It would be useful to investigate intraparticle entanglement between spin and orbital degrees of freedom in the chiral molecular system with different types of classical dynamics in the QD. Of particular interest is the spin degree of freedom in the weak SOC regime where, as existing studies suggested, it is possible to use classical chaos to enhance SO entanglement significantly at the expense of spin coherence. − …”

“…A potential approach is to exploit a hybrid structure that couples a chiral molecule to a 2D QD to form a "super chiral molecule" to control and manipulate spin polarization, as illustrated schematically in Figure 28. The idea originates from recent studies to control spin polarization by exploiting classical chaotic dynamics 370,371 and spin Fano resonances. 372 The role of classical dynamics in spin transport is intriguing from the point of view of a classical-quantum correspondence, as spin is a purely relativistic quantum mechanical variable.…”