Interlayer hybridization and magnetocaloric nodal rings in honeycomb bilayer magnets

We investigate the low-energy excitations and thermodynamic response of a spin- 1 / 2 transverse-field Ising antiferromagnet on a honeycomb bilayer with momentum-selective interlayer magnon hybridization. The interlayer coupling is constructed from three symmetry-related channels connecting equivalent sublattices in opposite layers. Their interference generates a 𝐶 3 -symmetric form factor, which makes the bilayer hybridization momentum dependent while preserving crystal momentum. Starting from the canted antiferromagnetic state of the individual layers, we employ linear spin-wave theory and diagonalize the resulting bosonic Bogoliubov–de Gennes Hamiltonian. We show that the momentum-dependent interlayer form factor reconstructs the low-energy magnon bands, producing softened branches and nodal-ring structures. The associated enhancement of the low-energy density of states generates pronounced entropy peaks and a tunable magnetic Grüneisen response. Our results identify nonlocal, momentum-selective interlayer hybridization as a route for engineering magnon spectra and magnetocaloric properties in layered quantum magnets.