Microscopic Identification of the D-vector in Triplet Superconductor Sr₂RuO₄

Abstract

Triplet superconductivity in Sr₂RuO₄ is investigated with main interest on its internal degree of freedom. We perform a microscopic calculation to investigate how the chiral state \\hatd(k)=(k_x±ik_y)\\hatz is realized among the underlying six degenerate states. Starting from the three band Hubbard model with spin–orbit interaction, we use a perturbation theory in order to calculate the pairing interaction. The p-wave superconductivity with T_c∼1.5 K is obtained in the moderately weak coupling region. It is shown that the orbital dependent superconductivity (ODS) robustly appears in Sr₂RuO₄. We determine the stabilized state by solving the Eliashberg equations. We find that the Hund coupling term as well as the spin–orbit interaction is necessary for the “symmetry breaking interaction”. The main result is that the chiral state is stabilized in case of the p-wave symmetry with the main γ-band, which is obtained in the perturbation theory. When we assume the other pairing symmetry including the f-wave state, the symmetry breaking interaction gives the other d-vector. The electronic structure constructed from the t_2g-orbitals is essential for this result.