Inelastic neutron scattering studies on 1D near-Heisenberg antiferromagnets: A test of the Haldane conjecture

Our studies of the spin dynamics for two near-Heisenberg antiferromagnets (AFMs) revealed: In CsNiCl3 (S=1) at low T≪TN we confirm the conclusions given earlier, but disagreement with the spin-wave calculations used is found for the eigenvectors. For TTN, the most important result is the observation that all 〈SαSα〉 (α=x,y,z) are identical, demanding another interpretation for the gap observed than the easy axis one. In CsVCl3 (S= (3)/(2) ) we could not observe any inconsistency in the microscopic parameters determined above and below TN. Although there is a striking coincidence with Haldane’s conjecture unexplained gap for S=1 (CsNiCl3), no such gap for S= (3)/(2) (CsVCl3), it is not clear whether this can be considered a proof for Haldane’s conjecture.