Nonunitary triplet pairing in the noncentrosymmetric superconductor LaNiC2

We present a first-principles based semiphenomenological approach to study the superconductivity in the noncentrosymmetric superconductor LaNiC2 with spin–orbit coupling. Based on group theoretical considerations, it was already shown that the breaking of time-reversal symmetry is only compatible with nonunitary triplet pairing states. To investigate the pairing mechanism by which this comes about and the possible role of the lack of inversion symmetry, we have combined the relativistic spin-polarized version of Korringa–Kohn–Rostoker method for the solution of the Dirac–Bogoliubov–de Gennes equations with a semiphenomenological parametrization of the pairing interaction. This made possible to study different orbital specific pairing models in quantitative details. We compare our predictions for the temperature dependence of the specific heat and it is found that it can be described by an interorbital equal-spin pairing on the nickel which breaks the time-reversal symmetry

Gap anisotropy in multiband superconductors based on multiple scattering theory

We implement the Bogoliubov-de Gennes equation in a screened Korringa-Kohn-Rostoker method for solving, self-consistently, the superconducting state for three-dimensional crystals. This method combines the full complexity of the underlying electronic structure and Fermi surface geometry with a simple phenomenological parametrization for the superconductivity. We apply this theoretical framework to the known s-wave superconductors Nb, Pb, and MgB2. In these materials multiple distinct peaks at the gap in the density of states were observed, showing significant gap anisotropy which is in good agreement with experiment. Qualitatively, the results can be explained in terms of the k-dependent Fermi velocities on the Fermi surface sheets exploiting concepts from BCS theory