Thermodynamic properties of the Haldane spin chain: a statistical model for the elementary excitations

Abstract

The low-temperature behaviour of the thermodynamic quantities in the one-dimensional 1D antiferromagnet with a Haldane ground state was analysed using a concept of non-interacting quasiparticles as a starting point. The proposed description appeared to be in good agreement with the results of the Monte Carlo study of a 128-site spin chain and experimental data obtained in NENP (Ni(C2H8N2)2NO2ClO4) provided that the elementary excitations constituting the Haldane triplet obey Fermi statistics.