Abstract
The ground state and thermodynamic properties of spin-1 and spin- chains are investigated via exactly solvedsu(3) and su(4) models with physically motivated chemical potential terms. The analysis involves thethermodynamic Bethe ansatz and the high temperature expansion (HTE) methods. For thespin-1 chain with large single-ion anisotropy, a gapped phase occurs which is significantlydifferent from the valence-bond-solid Haldane phase. The theoretical curves for themagnetization, susceptibility and specific heat are favourably compared withexperimental data for a number of spin-1 chain compounds. For the spin- chain a degenerate gapped phase exists starting at zero external magnetic field. A middlemagnetization plateau can be triggered by the single-ion anisotropy term. Overall, ourresults lend further weight to the applicability of integrable models to the physics oflow-dimensional quantum spin systems. They also highlight the utility of the exact HTEmethod.
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