Magnetic Excitations in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl$_2$-4SC(NH$_2$)$_2$

摘要

NiCl$_2$-4SC(NH$_2$)$_2$ (DTN) is a quantum S=1 chain system with strongeasy-pane anisotropy and a new candidate for the Bose-Einstein condensation ofthe spin degrees of freedom. ESR studies of magnetic excitations in DTN infields up to 25 T are presented. Based on analysis of the single-magnonexcitation mode in the high-field spin-polarized phase and previousexperimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set ofspin-Hamiltonian parameters is obtained. Our results yield $D=8.9$ K, $J_c=2.2$K, and $J_{a,b}=0.18$ K for the anisotropy, intrachain, and interchain exchangeinteractions, respectively. These values are used to calculate theantiferromagnetic phase boundary, magnetization and the frequency-fielddependence of two-magnon bound-state excitations predicted by theory andobserved in DTN for the first time. Excellent quantitative agreement withexperimental data is obtained.