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arXiv:cond-mat/9608062 · Physica A Statistical Mechanics and its Applications

Moment approach for the 2D attractive Hubbard model

José Jesús Rodríguez-Núñez, C.E. Cordeiro, A. Delfino

Published Oct 1, 1996• 1 citation
arXivHTMLPDF
DOI
10.1016/0378-4371(96)00212-9

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We constructed the one-particle spectral functions (diagonal and off-diagonal) which reproduce BCS for weak coupling and which take into account the effect of correlations on superconductivity in the attractive Hubbard model. The diagonal spectral function is composed of three peaks and the off-diagonal one is composed of two peaks. This ansatz satisfies the sum rules for the first six moments. Our solutions are valid for intermediate coupling, i.e., for U/t ≈ −4.0. Our set of analytical equations for the unknown variables is self-consistent and has been solved numerically in lowest order of the order parameter. As a result, we obtain that the presence of the third band, or upper Hubbard band, strongly renormalizes the two lower bands, making that the energy gap be k-dependent while the order parameter is pure s-wave. This shows that the order parameter and the gap are two different quantities.
We present strong numerical evidence for the band Kondo effect in the doped 2D Hubbard model by showing the systematic change of the density of states, imaginary part of the self-energy, effective magnetic moment and quasiparticle residue upon decreasing the temperature. Quadratically vanishing (in frequency) scattering rates near the Fermi energy and a linearly vanishing (in temperature) effective magnetic moment at low temperatures strongly support the screening of magnetic moments from singly occupied electrons by doped holes in the 2D Hubbard model.