Atomistic spin dynamics simulations of magnonic spin Seebeck and spin Nernst effects in altermagnets

TL;DR

This study uses atomistic spin dynamics simulations based on ab initio calculations to explore magnonic spin Seebeck and Nernst effects in altermagnets, revealing significant spin currents driven by thermal gradients.

Contribution

First quantitative simulation of magnonic spin transport phenomena in altermagnets using ab initio based atomistic spin dynamics.

Findings

Substantial spin Seebeck and Nernst effects observed.

Spin currents depend on magnon propagation direction.

Results align with symmetry and theoretical predictions.

Abstract

Magnon band structures in altermagnets are characterized by an energy splitting of modes with opposite chirality, even in the absence of applied external fields and relativistic effects, due to an anisotropy in the Heisenberg exchange interactions. We perform quantitative atomistic spin dynamics simulations based on ab initio electronic structure calculations on rutile RuO$_2$, a prototypical "d-wave" altermagnet, to study magnon currents generated by thermal gradients. We report substantial spin Seebeck and spin Nernst effects, i.e., longitudinal or transverse spin currents, depending on the propagation direction of the magnons with respect to the crystal, together with a finite spin accumulation associated with non-linearities in the temperature profile. Our findings are consistent with the altermagnetic spin-group symmetry, as well as predictions from linear spin wave theory and semiclassical Boltzmann transport theory.