Spin-split magnon bands induce pure spin current in insulating altermagnets

TL;DR

This paper develops a quantum-kinetic theory to analyze thermally driven magnon currents in altermagnets, revealing spin-split magnon bands that generate pure spin currents with potential for magnetization switching.

Contribution

It introduces a new theoretical framework for magnon transport in altermagnets, highlighting the role of spin-split bands in generating pure spin currents.

Findings

Prediction of a sizable magnon spin-splitting angle (~3.3 degrees)

Demonstration of pure transverse spin currents capable of exerting spin-splitter torque

Identification of intrinsic and extrinsic contributions to magnon Nernst and Seebeck effects

Abstract

Altermagnets offer a promising platform for dissipationless spin transport by combining zero net magnetization with spontaneous non-relativistic spin splitting. However, their magnonic transport properties remain largely unexplored. Here, we develop a quantum-kinetic theory for thermally driven magnon currents that cleanly separates Berry-curvature-driven intrinsic contributions from Drude-like scattering-dependent terms. Applying this framework to a collinear honeycomb antiferromagnet with anisotropic next-nearest-neighbor exchange and Dzyaloshinskii-Moriya interaction, we reveal spin-split magnon bands that support both intrinsic and extrinsic spin Nernst and Seebeck currents. For realistic parameters, we predict a sizable magnon spin-splitting angle (about 3.3 degrees) and a pure transverse spin current capable of exerting a strong spin-splitter torque suitable for magnetization switching.