In order to explore how superconductivity arises when charge fluctuations and spin fluctuations coexist, we have obtained a phase diagram against the off-site repulsion $V$ and band filling $n$ for the extended, repulsive Hubbard model on the square lattice with the fluctuation exchange approximation. We have found the existence of (i) a transition between $d_{xy}$ and $d_{x^2-y^2}$ pairing symmetries, (ii) $f$-pairing in between the $d_{x^2-y^2}$ and CDW phases for intermediate $0.5<n<1.0$ and large $V$, and (iii) for anisotropic cases the pairing symmetry changing, in agreement with a previously proposed “generic phase diagram,” as $d\to f\to s$ when $V$ (hence the charge fluctuations) are increased. All these are consequences of the structure in the charge and spin susceptibilities, which have peaks habitating at common or segregated positions in $k$ space.

• Received 16 December 2003

DOI:https://doi.org/10.1103/PhysRevB.70.094523