Field-tunable topological magnon–phonon hybridization and transverse thermal response in a FePSe3-inspired layered antiferromagnet

We develop a periodic low-energy effective framework for field-tunable magnon–phonon hybridization in layered antiferromagnetic systems inspired by FePSe ₃ 3 . The model retains a resonant magnon branch, an optical phonon branch, and a chirality-dependent complex coupling defined on a two-dimensional periodic momentum domain. This reduced description captures avoided crossings, hybridization-gap formation, and localized Berry-curvature structure in the coupled quasiparticle spectrum. The external field shifts the effective magnon branches differently in the two chirality sectors, thereby modifying the resonance condition and driving a field-controlled reconstruction of the hybrid bands. Using a gauge-invariant Fukui–Hatsugai–Suzuki calculation, we obtain integer-valued Chern numbers and identify a field-driven topological transition associated with a hybrid-gap closing and reopening in one effective sector. The low-field regime is characterized by opposite sector-resolved Chern numbers and a vanishing total lower-band Chern number, whereas the higher-field regime exhibits a total lower-band Chern number of $$-2$$ - 2 . We further evaluate a normalized transverse thermal response that incorporates the momentum-resolved Berry curvature, hybrid-band energies, and bosonic occupation factors. The response vanishes at zero field within the adopted parametrization and becomes finite when the field lifts the energetic balance between opposite chirality sectors. The results provide a reproducible proof of principle for how chirality-selective magnon–phonon hybridization can generate field-tunable hybrid-band topology and transverse thermal response in FePSe ₃ 3 -inspired antiferromagnets, without claiming a fully microscopic quantitative prediction for the complete material.