Superconductivity in the orbital degenerate model for heavy fermion systems

The magnetism and superconductivity of the new heavy fermion compounds CeTIn₅ (T = Co, Rh and Ir) are investigated by applying fluctuation exchange approximation to an orbital degenerate Hubbard model. The superconducting phase with d_x²−y² symmetry is found to appear next to the antiferromagnetic phase with increasing the orbital splitting energy. The present theory suggests that the orbital splitting energy plays a key role as a controlling parameter for the quantum phase transitions in the heavy fermion system.