Multiple bound states in the spin-1/2chain with Ising/Heisenberg/XY exchange

Abstract
Bound states and multiple bound states are studied in a linear chain of N spin=1/2 atoms with anisotropic exchange, using the Bethe method. Some analytic results are presented for the infinite chain together with a large number of numerical results for chains of eight and twelve atoms. The breakup of isolated bound states occurs by successively splitting off 'free' magnons as the anisotropy varies. Similar behaviour occurs with the multiple bound states although in one case a strong interaction between a bound state and a 'free' magnon was observed.
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