Studying magnon band topology through low-energy magnon excitations: role of anisotropic Dzyaloshinskii-Moriya interaction (2311.07201v3)

Abstract: In this work, we study topological properties of magnons via creating spin excitations in both ferromagnets and antiferromagnets in presence of an external magnetic field on a two-dimensional square lattice. It is known that Dzyaloshinskii-Moriya interaction (DMI) plays an important role in coupling between different particle (spin excitation) sectors, here we consider an anisotropic DMI and ascertain the role of the anisotropy parameter in inducing topological phase transitions. While the scenario, for dealing with ferromagnets, albeit with isotropic DMI is established in literature, we have developed the formalism for studying magnon band topology for the antiferromagnetic case. The calculations for the ferromagnetic case are included to facilitate a comparison between the two magnetically ordered systems. Owing to the presence of a two-sublattice structure of an antiferromagnet, a larger number of magnon bands participate in deciding upon the topological properties. However, in both the cases, an extended trivial region is observed even with the DMI to be non-zero, which is surprising since the DMI is the origin of the finite Berry curvature in presence of external magnetic field. Furthermore, in an antiferromagnet, a smaller anisotropy is capable of inducing a gap-closing transition from a topological to a trivial phase compared to that for a ferromagnet. The nature of the phases in both the cases and the phase transitions therein are characterized by the band structure, presence (or absence) of the chiral edge modes observed in a semi-infinite nano-ribbon geometry, computation of the thermal Hall effect, etc. Moreover, the strength of the magnetic field is found to play a decisive role in controlling the critical point that demarcates various topological phases.