Motion of bound domain walls in a spin ladder |
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Authors: | I Bose and A K Pal |
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Institution: | (1) University of Manchester, School of Mathematics, Oxford Road, M13 9PL Manchester, UK;(2) Health Methodology Research Group, University of Manchester, School of Community-Based Medicine, Jean McFarlane Building, University Place, M13 9PL Manchester, UK; |
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Abstract: | The elementary excitation spectrum of the spin-
\frac12\frac{1}{2} antiferromagnetic (AFM)
Heisenberg chain is described in terms of a pair of freely propagating spinons. In the
case of the Ising-like Heisenberg Hamiltonian spinons can be interpreted as domain walls (DWs)
separating degenerate ground states. In dimension d > 1, the issue of spinons as elementary
excitations is still unsettled.
In this paper, we study two spin-
\frac12\frac{1}{2} AFM ladder models
in which the individual chains are described by the Ising-like Heisenberg
Hamiltonian. The rung exchange interactions are assumed to be pure Ising-type in
one case and Ising-like Heisenberg in the other. Using the low-energy
effective Hamiltonian approach in a perturbative formulation, we show
that the spinons are coupled in bound pairs. In the first model, the
bound pairs are delocalized due to a four-spin ring exchange term
in the effective Hamiltonian. The appropriate dynamic structure factor
is calculated and the associated lineshape is found to be almost symmetric
in contrast to the 1d case. In the case of the second model, the bound
pair of spinons lowers its kinetic energy by propagating between chains.
The results obtained are consistent with recent theoretical studies
and experimental observations on ladder-like materials. |
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Keywords: | |
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