Anisotropic Superconductivity Emerging from the Orbital Degrees of Freedom in a Γ3 Non-Kramers Doublet System

We study superconductivity in a three-orbital model for f² ions with the Γ₃ crystalline electric field (CEF) ground state. An antiferromagnetic interaction between the Γ₇ and Γ₈ orbitals is introduced to stabilize the Γ₃ CEF state. This interaction also works as an on-site attractive interaction for spin-singlet pairing between electrons in these orbitals. The interorbital pairing state composed of the Γ₇ and Γ₈ orbitals on the same site has the E_g symmetry. Indeed, by applying the random phase approximation, we find that the E_g spin-singlet superconducting state is realized over a wide parameter range.