Refined Spin Wave Model and Multi-magnon Bound States in $Li_{2}CuO_{2}$

Abstract

Here we report a study of the spin dynamics in the ferromagnetic chain compound Li2CuO2. Inelastic neutron scattering measurements allow for the spin Hamiltonian to be determined using a J1 − J2 XXZ-Heisenberg spin chain model with weak inter-chain interactions. The primary exchange parameters determined from our data are qualitatively consistent with those of W. E. A. Lorentz et al. Europhys. Lett. 88, 37002 (2009), and our data allow for the resolution of additional inter-chain exchange interactions. We also observe the formation of two-and three-magnon bound states, stabilized by the weak, Ising-like exchange anisotropy of the nearestneighbor intra-chain interaction. While the two-magnon bound state exists only in the magnetically ordered phase of this material, the three-magnon state persists in a finite temperature regime above TN , indicating an unconventional character. Our results establish Li2CuO2as an experimental platform for the study of exchange anisotropy-stabilized bound states in a ferromagnetic chain.