Antiferromagnetic fluctuations, symmetry and shape of the gap function in the electron-doped superconductors: the functional renormalization-group analysis

The problem of the symmetry of the superconducting pairing and the form of the gap function in the electron-doped superconductors is reconsidered within the temperature-cutoff functional renormalization group approach combined with the Bethe-Salpeter equations. The momentum dependence of the order parameter for antiferromagnetic and superconducting instabilities in these compounds is analyzed. The gap function in the antiferromagnetic (particle-hole) channel has its maxima at the hot-spots, or at the diagonal of the Brilloin zone in their absence. The wavefunction in the singlet superconducting channel is non-monotonic in the vicinity of the (pi,0) and (0,pi) points, in striking similarity with recent experimental data. An instability in the triplet superconducting channel is much weaker than the singlet one and has an f-wave like form of the gap function.