Effects of carrier density and interactions on pairing symmetry in a t_2g model

By utilizing the fluctuation exchange approximation method, we perform a study on the superconducting pairing symmetry in a t_2g three-orbital model on the square lattice. Although the tight-binding parameters of the model are based on Sr₂RuO₄, we have systematically studied the evolution of superconducting pairing symmetry with the carrier density and interactions, making our findings relevant to a broader range of material systems. Under a moderate Hund’s coupling, we find that spin fluctuations dominate the superconducting pairing, leading to a prevalent spin-singlet pairing with a d_x²–y²-wave symmetry for the carrier density within the range of n = 1.5–4 per site. By reducing the Hund’s coupling, the charge fluctuations are enhanced and play a crucial role in determining the pairing symmetry, leading to a transition of the pairing symmetry from the spin-singlet d_x²–y²-wave to the spin-triplet p-wave. Furthermore, we find that the superconducting pairings are orbital dependent. As the carrier density changes from n = 4 to n = 1.5, the active orbitals for superconducting pairing shift from the quasi-two-dimensional orbital d_xy to the quasi-one-dimensional orbitals d_xz and d_yz.