SYMMETRY-INDUCED CORRELATION-EFFECTS AND HOLE PAIRING IN THE CU5O4 MODEL CLUSTER

We discuss the unique electronic properties of small clusters having a degenerate ground state in the non-interacting limit. We show that do ping holes in a Cu5O4 planar cluster may attract themselves in the pre sence of purely repulsive on-site interactions and discuss analogies a nd differences with the prototypical CuO4 case. Unlike other electroni c mechanisms proposed so far, this effect is due to the symmetry of th e system and does not rely on off-site interactions; moreover hole pai ring involves a change in the symmetry of the ground state. (C) 1997 E lsevier Science Ltd.