Topological characterization of magnon-polaron bands and thermal Hall conductivity in a frustrated kagome antiferromagnet

TL;DR

This paper explores how optical phonons coupled with magnons in a frustrated kagome antiferromagnet induce topological phase transitions and affect thermal Hall conductivity, using an analytic spin-Peierls transformation approach.

Contribution

It introduces a novel analytic framework for studying magnon-polaron bands in frustrated magnets with local and non-local spin-phonon couplings, revealing topological phase transitions.

Findings

Magnon-polaron bands exhibit topological phase transitions driven by spin-phonon coupling strength.

Thermal Hall conductivity varies significantly across different topological phases.

Bulk and edge spectral properties confirm the topological nature of the phases.

Abstract

Spin-phonon coupling and its efficacy in inducing multiple topological phase transitions in a frustrated kagome antiferromagnet have been rare in literature. To this end, we study the ramifications of invoking optical phonons in such a system via two different coupling mechanisms, namely, a local and a non-local one, which are distinct in their microscopic origin. In case of the local spin-phonon coupling, a single phonon mode affects the magnetic interactions, whereas in the non-local case, two neighbouring phonon modes are involved in the energy renormalization, and it would be worthwhile to compare and contrast between the two. To tackle these phonons, we propose an analytic approach involving a canonical spin-Peierls transformation applied to magnons. The formalism renders a hybridization between the magnons and the phonon modes, yielding magnon-polaron quasiparticles. In both the coupling regimes, validations for the topological signatures are systematically derived from the bulk and edge spectral properties of the magnon-polaron bands that are characterized by their corresponding Chern numbers. Thereafter, we investigate transitions from one topological phase to another solely via tuning the spin-phonon coupling strength. Moreover, these transitions significantly impact the behavior of the thermal Hall conductivity that aids in discerning distinct topological phases. Additionally, the explicit dependencies on the temperature and the external magnetic field are explored in inducing topological phase transitions associated with the magnon-polaron bands. Thus, our work serves as an ideal platform to probe the interplay of frustrated magnetism and polaronic physics.