Thermodynamic properties of the Δ-chain model in a uniform magnetic field

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Abstract
A numerical approach for calculating an eigenvalue distribution function is developed and it is applied to the study on a fully frustrated spin system called the Δ-chain model. We examine the magnetic-field dependence of the specific heat to clarify the relationship between the highly frustrated spins and the lower-temperature peak which has been extensively investigated by Kubo. Our numerical data show that with the increase of magnetic field, the peak width becomes broader and the height lower. This sensitive dependence should be caused by lowering the high degeneracy of states contributing to the peak formation. On the other hand, we also find that the higher-temperature peak observed commonly in antiferromagnetic quantum spin chains is almost unchanged.