Linear-response theory of the longitudinal spin Seebeck effect

TL;DR

This paper presents a linear-response theoretical framework for the longitudinal spin Seebeck effect, explaining how strong electron-phonon interactions can reverse the sign of spin injection signals, aligning with recent experimental observations.

Contribution

It introduces a linear-response theory for the longitudinal spin Seebeck effect that accounts for sign reversal due to electron-phonon interactions, a novel insight in the field.

Findings

Sign reversal of spin injection signal explained by theory

Electron-phonon interaction influences spin Seebeck effect

Theoretical results match recent experimental observations

Abstract

We theoretically investigate the longitudinal spin Seebeck effect, in which the spin current is injected from a ferromagnet into an attached nonmagnetic metal in a direction parallel to the temperature gradient. Using the fact that the phonon heat current flows intensely into the attached nonmagnetic metal in this particular configuration, we show that the sign of the spin injection signal in the longitudinal spin Seebeck effect can be opposite to that in the conventional transverse spin Seebeck effect when the electron-phonon interaction in the nonmagnetic metal is sufficiently large. Our linear-response approach can explain the sign reversal of the spin injection signal recently observed in the longitudinal spin Seebeck effect.