95-21 Bruno Nachtergaele
Bounds on the mass gap of the ferromagnetic XXZ chain (79K, LaTeX, 1 figure appended as uuencoded compressed Postscript file) Jan 23, 95
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Abstract. We prove rigorous lower and upper bounds for the mass gap of the ferromagnetic spin 1/2 XXZ chain. The two bounds coincide asymptotically in the Ising limit $\Delta\to\infty$. Near the isotropic point, $\Delta=1$, the estimates are good enough to determine the critical behaviour of the mass gap unambiguously. The derivation does not rely on exact solutions.

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