Essential model parameters for nonreciprocal magnons in multisublattice systems

TL;DR

This paper provides a theoretical framework to understand nonreciprocal magnon dispersions in multisublattice systems, identifying key microscopic parameters and interactions responsible for antisymmetric dispersion features.

Contribution

It introduces an analytical approach based on the Bogoliubov Hamiltonian to determine nonreciprocal magnon dispersions without solving eigenvalue problems, highlighting the roles of Dzyaloshinskii-Moriya and anisotropic interactions.

Findings

Analytical formulas for magnon dispersions derived from the Bogoliubov Hamiltonian.

Identification of antisymmetric interactions as sources of nonreciprocity.

Validation of the formulas for both ferromagnetic and antiferromagnetic systems.

Abstract

We theoretically investigate the microscopic conditions for emergent nonreciprocal magnons toward unified understanding on the basis of a microscopic model analysis. We show that the products of the Bogoliubov Hamiltonian obtained within the linear spin wave approximation is enough to obtain the momentum-space functional form and the key ingredients in the nonreciprocal magnon dispersions in an analytical way even without solving the eigenvalue problems. We find that the odd order of an effective antisymmetric Dzyaloshinskii-Moriya interaction and/or the even order of an effective symmetric anisotropic interaction in the spin rotated frame can be a source of the antisymmetric dispersions. We present possible kinetic paths of magnons contributing to the antisymmetric dispersions in the one- to four-sublattice systems with the general exchange interactions. We also test the formula for both ferromagnetic and antiferromagnetic orderings in the absence of spatial inversion symmetry.