Cryogenic spin Seebeck effect

TL;DR

This paper develops a microscopic quantum noise model to analyze the non-linear behavior of the spin Seebeck effect in ferromagnetic nanowires at cryogenic temperatures, revealing sign changes in transverse SSE and stability in longitudinal SSE.

Contribution

It introduces a quantum noise-based microscopic model to explain non-linearities and sign changes in the spin Seebeck effect at cryogenic temperatures.

Findings

Transverse SSE changes sign with temperature and gradient at specific detector positions.

Longitudinal SSE remains stable and linear outside the linear response regime.

The model explains non-linearities observed in cryogenic spin caloritronics.

Abstract

We present a theory of the non-linearities of the spin Seebeck effect (SSE) in a ferromagnetic nanowire at cryogenic temperatures. We adopt a microscopic quantum noise model based on a collection of two-level systems. At certain positions of Pt detectors to the wire, the transverse SSE changes sign as a function of temperature and/or temperature gradient. On the other hand, the longitudinal SSE does not show significant non-linearities even far outside the regime of validity of linear response theory.