Pairing Mechanism and Anisotropy of d-Vector of Spin-Triplet Superconductor Sr2RuO4

The anisotropy of the d-vector of the spin-triplet superconductor Sr2RuO4 is investigated on the basis of a d-p model where the Coulomb interaction U-pp at the O site is taken into account together with U-dd at the Ru site. It is shown in the third-order perturbation for the pairing interaction that U-pp induces the spin-triplet pairing of (sin p(x) + i sin p(y)) symmetry. The piaring State with the d-vector in the RuO2 plane is stabilized by the atomic spin-orbit interaction and Hund's rule coupling at the Ru site, in contrast to the result based on the multiband Hubbard model without U-pp. This result is consistent with that obtained by the Knight shift measurement.