Magnon Splitting and Magnon Spin Transport in Altermagnets

Altermagnets, a new type of collinear antiferromagnet, exhibiting non-degenerate electron and magnon dispersion in momentum space have attracted intensive research attention. We theoretically analyze the origin and feature of chiral magnon splitting in representative altermagnets including tetragonal RuO_2, hexagonal MnTe, and orthorhombic LaMnO_3. The magnon spin transport properties including spin Seebeck and spin Nernst coefficients have been investigated. Through these materials, we demonstrate the difference of chiral splitting in d-wave and g-wave antiferromagnet on magnon transport. RuO_2 with planar magnon splitting exhibits significant magnon spin Nernst and magnon spin Seebeck anisotropy in (110) and (001) planes, whereas MnTe, due to its bulk-like magnon splitting, is incapable of producing magnon spin Nernst effect. Our work may provide in-depth understanding on the mechanisms of nonrelativistic magnon splitting and thermal spin transport in altermagnets.