Triplet pairing superconductivity induced by short-range ferromagnetic correlations in Sr2RuO4

The microscopic origin of triplet superconductivity in Sr2RuO4 is discussed, paying attention to the role of Coulomb interaction, U-pp, at the O site. It is shown on the d-p model that Upp induces a ferromagnetic exchange interaction between "d-electrons" (molecular orbital with d(xy)-symmetry) at adjacent Ru sites, leading to short-range ferromagnetic correlations and promoting Cooper pairing with (sin p(x) +/- i sin p(y))-syrnmetry on the gamma-band. The reason why such ferromagnetic Correlations work effectively may be traced back to the fact that the level of 4d-electrons at Ru sites is relatively low and located near that of 2p-electrons at O sites.