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

Abstract

Our studies of the spin dynamics for two near‐Heisenberg antiferromagnets (AFMs) revealed: In CsNiCl₃ (S=1) at low T≪T_N we confirm the conclusions given earlier, but disagreement with the spin‐wave calculations used is found for the eigenvectors. For T>T_N, the most important result is the observation that all 〈S^αS^α〉 (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 T_N. 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.