Charge Conjugation and Pairing in a model Cu$_{5}$O$_{4}$ Cluster

Michele Cini; Adalberto Balzarotti; Gianluca Stefanucci

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arXiv · cond-mat/9811116

Charge Conjugation and Pairing in a model Cu$_{5}$O$_{4}$ Cluster

Michele Cini·Adalberto Balzarotti·Gianluca Stefanucci

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Abstract

Highly-symmetric three-band Hubbard Cu-O clusters have peculiar properties when the hole number is such that they admit W=0 hole pairs. These are two-hole eigenstates of the on-site Hubbard repulsion with eigenvalue 0, get bound by correlation effects when dressed by the interaction with the background, and cause superconducting flux quantization. We study the Cu$_{5}$O$_{4}$ cluster by exact diagonalization and show that bound electron pairs of $^{1}$% B$_{2}$ symmetry are obtained at an appropriate filling, and quantize flux like the hole pairs. The basic mechanism for pairing in this model is the second-order exchange diagram, and an approximate charge conjugation symmetry holds between electron and hole pairs. Further, the flux quantization property requires that the W=0 pairs of $d$ symmetry have $s$ symmetry couterparts, still with W=0; the former are due to a spin fluctuation, while the latter arise from a charge fluctuation mechanism. The simultaneous existence of both is an essential property of our model and is required for any model of superconducting $d$ pairs.

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Michele Cini, Adalberto Balzarotti, Gianluca Stefanucci. 1998-11-09. Charge Conjugation and Pairing in a model Cu$_{5}$O$_{4}$ Cluster. https://arxiv.org/abs/cond-mat/9811116

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