Superconducting pairing of the extended multiband Hubbard model: A weak-coupling study

Pairing mediated by charge and spin fluctuations is examined within the weak-coupling approximation for a three-band Hubbard model for the cuparate superconductors with both intrasite ($U_d$,$U_p$) and intersite repulsion ($U_{\mathrm{pd}}$). Like in the one-band situation, paramagnon exchange near a spin-density-wave instability gives rise to a singlet d-wave pairing interaction. On the other hand, the exchange of charge-fluctuation modes due to $U_{\mathrm{pd}}$ leads to s-wave coupling near an interband instability and to d-wave coupling near the intraband charge-density-wave instability. When simultaneously on-site interactions are included the s-wave pairing is shifted to large dopings away from half-filling and again replaced by d-wave coupling for smaller dopings.