Green's function representation of spin pumping effect

TL;DR

This paper develops a Green's function-based theoretical framework to analyze spin pumping effects driven by external potentials, revealing the role of spin gauge fields and static potential analogies in strong exchange interactions.

Contribution

It introduces a Green's function formula for current pumping, linking spin gauge fields to spin current generation in systems with strong sd exchange interaction.

Findings

Pumping driven by changes in particle distribution.

Spin gauge field acts as a constant potential at low precession frequencies.

System reduces to a static problem with off-diagonal spin components.

Abstract

In this study, current pumping by an external potential is studied on the basis of the Keldysh Green's function method, and a pumping formula written in terms of retarded and advanced Green's functions is obtained. It is shown that pumping is essentially driven by a change of particle distribution before and after an external perturbation. The formula is used to study the spin pumping effect in the case of strong sd exchange interaction, and the driving field is identified to be the spin gauge field. At the lowest order in the precession frequency of magnetization, the spin gauge field works as a constant potential, and the system is shown to reduce to a static problem of spin current generation by a time-independent potential with off-diagonal spin components.