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

Abstract

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 is based on $\rm Sr_2RuO_4$, 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 $d_{x^2-y^2}$-wave symmetry for the carrier density within the range of $n=1.5\sim4$ 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 $d_{x^2-y^2}$-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 $d_{yz}$.