Spin-Triplet Superconductivity due to Antiferromagnetic Spin-Fluctuation inSr2RuO4

A mechanism leading to the spin-triplet superconductivity is proposed based on the antiferromagnetic spin-fluctuation. The effects of anisotropy in spin-fluctuation on the Cooper pairing and on the direction of $\mathit{d}$ vector are examined in the one-band Hubbard model with random-phase approximation. The gap equations for the anisotropic case are derived and applied to ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. It is found that a nesting property of the Fermi surface together with the anisotropy leads to the triplet superconductivity with the $\mathit{d}=\mathit{ẑ}(\sin k_x\pm i\sin k_y)$, which is consistent with experiments.