Haldane-gap excitations in the low-Hc one-dimensional quantum antiferromagnet Ni(C5D14N2)2N3(PF6) -: art. no. 104410

Inelastic neutron scattering on deuterated single-crystal samples is used to study Haldane-gap excitations in the new S=1 one-dimensional quantum antiferromagnet Ni(C5D14N2)(2)N-3(PF6), that was recently recognized as an ideal model system for high-field studies. The Haldane gap energies Delta (x)=0.42(3) meV, Delta (y) = 0.52(6) meV, and Delta (t) = 1.9(1) meV, for excitations polarized along the a, b, and c crystallographic axes, respectively, are measured. The dispersion relation is studied for momentum transfers both along and perpendicular to the chains' direction. The in-chain exchange constant J = 2.8 meV is found to be much larger than interchain coupling, J(y) = 1.8(4) x 10(-3) meV and J(x) = 4(3) x 10(-4) meV, along the b and a axes, respectively. The results are discussed in the context of future experiments in high magnetic fields.