Magnon interactions in anisotropic Ising chains.

Experiments and simulations of the quasi-1D Ising-chain ferromagnet CoNb₂O₆ in a polarized transverse field have shown evidence of a quasiparticle breakdown. We use spin-wave theory beyond the linear treatment to capture magnon interactions in the paramagnetic phase. We investigate decay processes and unphysical divergences in the spin-flip spectrum produced by Van Hove singularities in the 2-magnon density of states, which are regularized via a self-consistent treatment. We further explore various symmetry-allowed exchange terms in the spin Hamiltonian that can be relevant to different Ising-like chains such as BaCo₂V₂O₈ and SrCo₂V₂O₈.