 99303 Oscar Bolina, Pierluigi Contucci, Bruno Nachtergaele, Shannon Starr
 Finitevolume excitations of the 111 interface in the quantum XXZ modelLatex
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Aug 19, 99

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Abstract. We show that the ground states of the threedimensional XXZ Heisenberg
ferromagnet with a 111 interface have excitations localized in a
subvolume of linear size R with energies bounded by O(1/R^2). As
part of the proof we show the equivalence of ensembles for the 111
interface states in the following sense: In the thermodynamic limit the
states with fixed magnetization yield the same expectation values for
gauge invariant local observables as a suitable grand canonical state
with fluctuating magnetization. Here, gauge invariant means commuting with
the total third component of the spin, which is a conserved quantity of
the Hamiltonian. As a corollary of equivalence of ensembles we also prove
the convergence of the thermodynamic limit of sequences of canonical
states (i.e., with fixed magnetization).
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