Support for the Haldane conjecture: Gap for magnetic excitations in the quasi-one-dimensionalS=1Heisenberg antiferromagnetAgVP2S6

Abstract

The low-temperature magnetic-excitation spectrum of polycrystalline ${\mathrm{AgVP}}_2$ ${\mathrm{S}}_6$ begins above a gap ($E_g$=27.4 meV) with a form typical of a one-dimensional singularity. Powder-diffraction patterns show no long-range magnetic order but only a diffuse feature consistent with one-dimensional magnetic correlations. These observations are in agreement with the prediction of Haldane concerning the quantum gap of one-dimensional Heisenberg antiferromagnets with integer values of spin.