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Physical review. B, Condensed matter

Excitations in a nearly half-filled Hubbard model withU=∞

S. E. Barnes

Published Jul 1, 1989• 6 citations
Publisher

Abstract

It is shown that, even near half filling, the elementary excitations of the large-U Hubbard model form wide bands of width \ensuremath{\sim}t, the intersite hopping integral, and that the slave-boson-based mean-field approximation is qualitatively wrong in the relevant limit. This large-U limit has no Kondo-type divergences.
DOI
10.1103/physrevb.40.723

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Following Nagaoka, the ground state of the large-U nearly half-filled Hubbard model is ``ferromagnetic.'' However, because of the anisotropic exchange energy JA{\mathit{J}}_{\mathit{A}}JA​, the physical Nagaoka ground state is nondegenerate and comprises a totally disordered spin state, i.e., a linear combination of all possible spin arrangements. For this ground state the susceptibility is Pauli-like but of a magnitude associated with a narrow band of width \ensuremath{\sim}JA{\mathit{J}}_{\mathit{A}}JA​ while the holons, i.e., the charge excitations, correspond to spinless fermions with a band of width 2zt. Associated with the spinon sector are very poorly defined spin waves, i.e., bosons, with a quadratic dispersion relation. These spin waves do not become soft at any finite temperature, rather, they soften as they approach the metal-insulator transition, i.e., as the number of holes n0{\mathit{n}}_{0}n0​ becomes small. Examined is the problem of constructing a mean-field slave-boson approach for the present problem.