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 Eg symmetry. Indeed, by applying the random phase approximation, we find that the Eg spin-singlet superconducting state is realized over a wide parameter range.