Sign Changes in Heat, Spin, and Orbital Magnon Transport Coefficients in Kitaev Ferromagnets

Abstract: Both Kitaev and Dzyaloshinskii-Moriya interactions (DMI) are known to promote intrinsic contributions to the magnon Hall effects such as the thermal Hall and the spin Nernst effects in collinear magnets. Previously, it was reported that a sign change in those transversal transport coefficients only appears in the presence of Kitaev interaction, but not for DMI, which qualitatively distinguishes both kinds of spin-anisotropic interactions in ferromagnets. Herein, we systematically study how the magnon-mediated heat, spin, and orbital transport in longitudinal and transverse geometries evolves with a continuously varying Kitaev-to-DMI ratio, but a fixed magnon band structure. We show that several transport coefficients feature temperature-driven sign changes in the presence of Kitaev interaction, which are absent for DMI. In particular, we find a sign change in longitudinal orbital transport, the magnon orbital Seebeck effect, which is absent in the transverse geometry, the magnon orbital Nernst effect. This sets the orbital transport apart from the heat and spin transport, where we only find sign changes promoted by the Kitaev interaction in transverse, but not in the longitudinal geometry.