Refined Spin Wave Model and Multi-magnon Bound States in $L{i}_{2}Cu{O}_2$

Abstract

Here we report a study of the spin dynamics in the ferromagnetic chain compound $L{i}_{2}Cu{O}_2$. Inelastic neutron scattering measurements allow for the spin Hamiltonian to be determined using a $J_1-J_2$ $XXZ$-Heisenberg spin chain model with weak interchain interactions. The primary exchange parameters determined from our data are qualitatively consistent with those of Lorenz $et$ $al.$ [Europhys. Lett. 88, 37002 (2009)], and our data allow for the resolution of additional interchain exchange interactions. We also observe the formation of two- and, potentially, three-magnon bound states. The two-magnon bound state exists only in the magnetically ordered phase of this material, consistent with stabilization by the weak, Ising-like exchange anisotropy of the nearest-neighbor intrachain interaction. In contrast, the potential three-magnon state persists in a finite temperature regime above $T_N$, indicating an unconventional character. Our results establish $L{i}_{2}Cu{O}_2$ as an experimental platform for the study of exchange anisotropy-stabilized bound states in a ferromagnetic chain.

13 pages, 9 figures

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Cited by in corpus (3)

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• High-accuracy evaluation of non-thermal magnetic states beyond spin-wave theory: applications to higher-energy states