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Elementary excitations in the gapped phase of a frustrated S=1/2 spin ladder: from spinons to the Haldane triplet

S. Brehmer·A. K. Kolezhuk·H. -J. Mikeska·U. Neugebauer
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Abstract

We use the variational matrix-product ansatz to study elementary excitations in the S=1/2 ladder with additional diagonal coupling, equivalent to a single S=1/2 chain with alternating exchange and next-nearest neighbor interaction. In absence of alternation the elementary excitation consists of two free S=1/2 particles ("spinons") which are solitons in the dimer order. When the nearest-neighbor exchange alternates, the "spinons" are confined into one S=1 excitation being a soliton in the generalized string order. Variational results are found to be in a qualitative agreement with the exact diagonalization data for 24 spins. We argue that such an approach gives a reasonably good description in a wide range of the model parameters.

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S. Brehmer, A. K. Kolezhuk, H. -J. Mikeska, U. Neugebauer. 1997-10-13. Elementary excitations in the gapped phase of a frustrated S=1/2 spin ladder: from spinons to the Haldane triplet. https://doi.org/10.1088/0953-8984%2F10%2F5%2F017

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