Magnon Thermal Hall Effect Induced By Symmetric Exchange Interaction

Abstract

By analyzing the spin-group symmetry of magnons, we establish two generalized Onsager's relations in the magnon thermal Hall effect, which reveals the rich and complicated structures of the magnon Berry curvature in the parameter space of different types of the exchange coupling. As an important consequence, we find that the diagonal and off-diagonal part of the symmetric anisotropic exchange coupling together can support the planar magnon thermal Hall effect without the DM interaction. This removes the local inversion-symmetry-breaking condition for generating the magnon thermal Hall effect. Moreover, we predict an exotic phenomenon that the thermal conductivity exhibits angular dependence with respect to the in-plane magnetization. Our work lays the ground for decoding the coupling between magnon transport and different types of exchange interactions.

Figures (2)

• Figure 1: DM interaction (a) and symmetric exchange interaction (b). In (a), the intermediate non-magnetic gray atom breaks the inversion and mirror-z symmetry. In (b), the mirror-x and mirror-y symmetry should be broken to have the symmetric coupling $S_{ix}S_{jy}+S_{iy}S_{jx}$. The mirror-z symmetry is allowed.
• Figure 2: Magnon thermal Hall effect from symmetric exchange interaction. (a) Antiferromagnetic honeycomb lattice, with mirror planes bisecting each nearest neighbor bond. The spin order is along the x direction. (b) The thermal conductivity as a function of parameter $\alpha$ with $\alpha$ being the angle of $J^-+i\Gamma$. The magnitude $\sqrt{(J^-)^2+\Gamma^2}$ is fixed. (c) Schematics of in-plane magnon thermal Hall effect. (d) Thermal conductivity as a function of the orientation of the in-plane ferromagnetic spin order aligned by external magnetic field.