Manipulation of magnonic topological phases via chirality injection

Abstract

In certain magnetic systems, magnon bands can exhibit topologically nontrivial phases, which are often referred to as magnonic topological insulators due to their similarities to electronic topological insulators. The conventional methods to manipulate the magnon-band topology have hitherto required the bulk manipulation of the systems via, e.g., the application of an external magnetic field. In this work, we lift the previous limitation of the magnon topology control on the bulk manipulation by showing that the magnon-band topology can be controlled from the boundary by injecting a spin chirality from the boundary into the bulk, which can be realized, e.g., by utilizing the proximate heavy metal and the resultant interfacial spin Hall effects. More specifically, we propose a scheme to manipulate magnonic topological phases of ferromagnets and antiferromagnets on a honeycomb lattice via chirality injection from the boundaries of the sample [1]. We find that the magnon Hamiltonian subjected to the spin chirality injection possesses a sublattice-symmetry-breaking mass term resulting from the coupling between the spin chirality and the Dzyaloshinskii-Moriya interaction on top of the previously studied bosonic counterpart of the Haldane model [2, 3]. This chirality-induced mass term competes with the known Haldane mass term, which allows us to nonlocally tune the bulk topology from nontrivial to trivial and vice versa by the boundary manipulation. For experimental probes of the chirality-induced topological phase transition, we propose the magnon thermal Hall effect arising from the band topology. The “shoulders” in the thermal Hall conductivity can herald the presence of the proposed phase boundary. Our work leads us to envision that the interfacial chirality injection may offer a nonintrusive means to manipulate the static and the dynamics bulk properties of general magnetic systems.