Superconducting pairs in clusters and in the Cu-O plane

Recently, by exact diagonalisation methods, we reported superconducting pai ring and flux quantization in Cu-O Hubbard clusters of up to 21 atoms. The pairing is due to a configuration interaction mechanism driven by symmetry, and arises when the least bound holes have vanishing mutual repulsion (W=0 pairs). The second-order, spin-flip interaction leads to a net attraction for the singlet and repulsion for the tripler. Here we show that electron b ound pairs also exist and show similar flux quantization properties. Then, we extend the theory of pairing to the full plane and to all orders.