Pairing correlations in a generalized Hubbard model for the cuprates

Using numerical diagonalization of a 4x4 cluster, we calculate on-site s, extended-s, and d(x2-y2) pairing correlation functions (PCF's) in an effective generalized Hubbard model for the cuprates, with nearest-neighbor correlated hopping and next-nearest-neighbor hopping t'. The vertex contributions to the PCF's are significantly enhanced, relative to the t-t'-U model. The behavior of the PCF's and their vertex contributions, and signatures of anomalous flux quantization, indicate superconductivity in the d-wave channel for moderate doping and in the s-wave channel for high doping and small U.