Spin-Fluctuation-Driven Orbital Nematic Order in Ru-Oxides: Self-Consistent Vertex Correction Analysis for Two-Orbital Model

To reveal the origin of the nematic electronic fluid phase in Sr3Ru2O7, we apply the self-consistent vertex correction analysis to the (d(xz), d(yz))-orbital Hubbard model. It is found that the Aslamazov-Larkin type vertex correction causes the strong coupling between spin and orbital fluctuations, which corresponds to the Kugel-Khomskii spin-orbital coupling in the local picture. Owing to this mechanism, orbital nematic order with C-2 symmetry is induced by the magnetic quantum criticality in multiorbital systems, whereas this mechanism is ignored in the random-phase-approximation (RPA). This study provides a natural explanation for the close relationship between the magnetic quantum criticality and nematic state in Sr3Ru2O7 and Fe-based superconductors.