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Journal of Physics Condensed Matter

On the excitations in a S=1 linear chain Heisenberg antiferromagnet with S=1/2impurities

Alexander V. Balatsky, Andrey V. Chubukov

Published Mar 11, 1991• 0 citations
Publisher

Abstract

It is argued that a S=1 linear chain Heisenberg antiferromagnet containing some amount of S= 1 / 2 impurities has integer-spin excitations, induced by doped spins. These excitations results from the breaking of a single valence bond on a site neighbouring the impurity.
DOI
10.1088/0953-8984/3/10/013

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The s=1 Heisenberg antiferromagnet is studied in the presence of two kinds of local impurities. First, a perturbed antiferromagnetic bond with J'\ensuremath{\ne}J at the center of an even-length open chain is considered. Using the density-matrix renormalization-group method we find that, for sufficiently strong or weak J', a bound state is localized at the impurity site, giving rise to an energy level in the Haldane gap. The energy of the bound state is in agreement with perturbative results, based on s=1/2 chain-end excitations, both in the weak- and strong-coupling limit. In a region around the uniform limit, J'=J, no states are found with energy below the Haldane gap. Second, a s=1/2 impurity at the center of an otherwise even-length open chain is considered. The coupling to the s=1/2 impurity is varied. Bound states in the Haldane gap are found only for sufficiently weak (antiferromagnetic) coupling. For a s=1/2 impurity coupled with a strong (antiferromagnetic) bond, no states are found in the Haldane gap. Our results are in good qualitative agreement with recent experiments on doped NENP and Y2{\mathrm{Y}}_{2}Y2​BaNiO5{\mathrm{BaNiO}}_{5}BaNiO5​.
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