Discretized excitation spectra by magnon confinement in quasi S=1 spin-chain systems

Quantized excitation spectra below the Neel temperature have been observed in recent inelastic neutron scattering measurements on (Ba/Sr) Co₂V₂O₈ [1-3]. Interestingly, negative zeros of the Airy functions (NZAF) well explain the energy dependence of peak positions in the spectra. Since the effective model for these compounds is considered to be S=1/2 antiferromagnetic Ising-like XXZ chains, two spinons in the excitation continuum can be confined by interchain couplings and thus, the spectra become discretized [4]. In this study, we focus on the S=1 spin chains that shows excitation continuum originated by magnons and investigate the possibility of discretization by the interchain couplings. We calculate dynamical spin structure factors by employing iTEBD method. From the numerical results, we find that the magnon continuum in the Haldane chain also shows the discretization. The peak position is explained by the NZAF only if the system is placed at the Ising limit, where the single ion anisotropy is quite strong in contrast to the Heisenberg interaction. [1]S. Kimura, et al., PRL 99, 087602 (2007). [2]Z. Wang, et al., PRB 91, 140404(R) (2015). [3]B. Grenier, et al., PRL 114, 017201 (2015). [4]H. Shiba, Prog. Theor. Phys. 64, 466 (1980).