Pairing interaction in CuO clusters

Abstract

We examine the tendency to pairing of holes added on CuO clusters with one hole per Cu as the reference state, for a variety of cluster geometries. The model Hamiltonian considered contains on-site and short-range Coulomb repulsion terms. Confirming and extending our previous results, we find a tendency to pairing for a wide range of parameters in the model Hamiltonian. The tendency to pairing arises from a disruption of the local order in the insulating system (with one hole per Cu) by addition of the extra holes. We discuss to what extent it is possible to identify the pairing mechanism as "charge mediated" or "spin mediated" as a function of the parameters. We examine the stability of the system with respect to real condensation (phase separation) in the regime where the pair interaction is attractive. Finally, we discuss the possible connection of our results to the superconductivity mechanism in high-$T_c$ oxides.