Exact diagonalization of a two-dimensional double band Hubbard model on a twelve-site CuO cluster

We present a numerical study of the two-dimensional double band Hubbard model on a twelve-site cluster simulating a copper-oxygen layer. The ground state is antiferromagnetic but magnetic ordering is greatly reduced by doping the cluster with extra holes. The presence of a positive extended-singlet pairing correlation supports a magnetic mechanism for an attractive interaction between holes on second neighbour oxygen sites.