Heavy-fermion system: Superconducting and magnetic fluctuations within a periodic-cluster Hubbard model

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Abstract
An exact solution of an eight-site crystal model with periodic boundary conditions, a small face-centered-cubic crystal, is presented for the case of a heavy-fermion system. The model consists of (a) single, fully symmetric orbital per site, with nearest-neighbor and second-nearest-neighbor hopping; (b) an infinite Coulomb repulsion between electrons on the same site; (c) antiferromagnetic superexchange interactions; and (d) band fillings near half filling (six, seven, and eight electrons per cluster). The superconducting and the antiferromagnetic correlations are studied and compared with the predictions of the noninteracting limit. The suitability of Bardeen-Cooper-Schrieffer and Gutzwiller approximate ground-state wave functions are quantitatively estimated.

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