Ground state of the three-dimensional BCS d-wave superconductor

We determine the mean-field ground state of the three-dimensional rotationally symmetric d-wave (l=2) superconductor at weak coupling. It is a noninert state, invariant under the symmetry C2 only, which breaks time-reversal symmetry almost maximally, and features a high but again less-than-maximal average magnetization. The state obtained by minimization of the expanded sixth-order Ginzburg–Landau free energy is found to be an excellent approximation to the true ground state. The coupling to a parasitic s-wave component has only a minuscule quantitative and no qualitative effect on the ground state.