Anomalous heat and spin transport induced by in-plane DM interaction in magnetic insulators

We discuss anomalous heat and spin transport induced by in-plane Dzyaloshinskii-Moriya interaction (DMI) in two-dimensional magnetic insulators with collinear out-of-plane magnetic order. In such magnets, the DMI does not appear in the linear spin wave theory, so that we usually do not expect the DMI to cause anomalous heat and spin transport. However, we find two mechanisms of anomalous transport that go against this expectation. First, the in-plane DMI can induce interaction between magnon phonon. Consequently, magnon and phonon states can hybridize when their energies coincide, resulting in Berry curvature in the anti-crossing regions between the magnon and phonon spectrum. As a result of the Berry curvature, we find nonzero thermal Hall and spin Nernst effect. Second, the in-plane DMI can induce anomalous heat and spin transport if we go beyond the linear spin wave theory. In particular, we find that the Schwinger boson mean field Hamiltonian of a two-dimensional ferromagnet is analogous to that of the two-dimensional electron gas with Rashba spin-orbit coupling. Therefore, we obtain a new platform to study bosonic analogues of the physics found in Rashba electron gas, such as anomalous Hall effect, spin Hall effect, and Rashba-Edelstein effect.