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arXiv · 1402.6087

Delta chain with ferromagnetic and antiferromagnetic interactions at the critical point

V. Ya. Krivnov·D. V. Dmitriev·S. Nishimoto·S. -L. Drechsler·J. Richter
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Abstract

We investigate the spin-1/2 Heisenberg model on the delta chain (sawtooth chain) with ferromagnetic nearest-neighbor and antiferromagnetic next-neighbor interactions. For a special ratio between these interactions there is a class of exact ground states formed by localized magnons and the ground state is macroscopically degenerate with a large residual entropy per spin $s_0=\frac{1}{2}\ln 2$. An important feature of this model is a sharp decrease of the gaps for excited states with an increase of the number of magnons. These excitations give an essential contribution to the low-temperature thermodynamics. The behavior of the considered model is compared with that of the delta chain with both antiferromagnetic interactions.

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V. Ya. Krivnov, D. V. Dmitriev, S. Nishimoto, S. -L. Drechsler, J. Richter. 2014-02-25. Delta chain with ferromagnetic and antiferromagnetic interactions at the critical point. https://doi.org/10.1103/physrevb.90.014441

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