1203.3576 (Fusayoshi J. Ohkawa)
Fusayoshi J. Ohkawa
The half-filled ground state of the Hubbard model on the hyper-cubic lattice in D dimensions is studied under and beyond supreme single-site approximation, which is none other than dynamical mean-field theory (DMFT), by Kondo-lattice theory, which is none other than 1/D expansion theory, but within the constrained Hilbert subspace where no symmetry is allowed to be broken. A gap can open in the single-particle excitation spectrum if and only if residual entropy is nonzero or entropy at T=+0K is nonzero. The Mott insulator with no symmetry broken, if it is possible, is characterized by nonzero residual entropy or nonzero entropy at T=+0K. This conclusion is never inconsistent with Brinkman and Rice's theory and DMFT, while it is inconsistent with the Bethe-ansatz solution for one dimension. Two possible explanations are given for the inconsistency.
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http://arxiv.org/abs/1203.3576
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