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Название: A Two-Dimensional Isotropic Quantum Antiferromagnet with Unique Disordered Ground State
Авторы: Kennedy T., Lieb E., Tasaki H.
We continue the study of valence-bond solid antiferromagnetic quantum Hamiltonians. These Hamiltonians are invariant under rotations in spin space. We prove that a particular two-dimensional model from this class (the spin-3/2 model on the hexagonal lattice) has a unique ground state in the infinite-volume limit and hence no Neel order. Moreover, all truncated correlation functions decay exponentially in this ground state. We also characterize all the finite- volume ground states of these models (in every dimension), and prove that the two-point correlation function of the spin-2 square lattice model with periodic boundary conditions has exponential decay.