Superconducting phase diagram in a model for tetragonal and cubic systems with strong antiferromagnetic correlations

We calculate the superconducting phase diagram as a function of temperature and z-axis anisotropy in a model for tetragonal and cubic systems having strong antiferromagnetic fluctuations. The formal basis for our calculations is the fluctuation exchange approximation applied to the single-band Hubbard model near half-filling. For nearly cubic lattices, two superconducting phase transitions are observed as a function of temperature with the low-temperature state having the time-reversal symmetry-breaking form d_x²−y²±id_3z²−r². With increasing tetragonal distortion, the time-reversal symmetry-breaking phase is suppressed, giving way to only d_x²−y² or d_3z²−r² single-component phases. Based on these results, we propose that a time-reversal symmetry-breaking superconducting state may be found in cubic systems with pairing driven by antiferromagnetic fluctuations.