Symmetry, Nodal Structure, And Bogoliubov Fermi Surfaces For Nonlocal Pairing

Multiband effects can lead to fundamentally different electronic behavior of solids, as exemplified by the possible emergence of Fermi surfaces of Bogoliubov quasiparticles in centrosymmetric superconductors which break time-reversal symmetry. We extend the analysis of possible pairing symmetries, the corresponding nodal structure, and the Bogoliubov Fermi surfaces in two directions: we include nonlocal pairing and we consider internal degrees of freedom other than the effective angular momentum of length j = 3/2 examined so far. Since our main focus is on the Bogoliubov Fermi surfaces, we concentrate on even-parity pairing. The required symmetry analysis is illustrated for several examples, as a guide for the reader. We find that the inclusion of nonlocal pairing leads to a much larger range of possible pairing symmetries. For infinitesimal pairing strength, we find a simple yet powerful criterion for nodes in terms of a scalar product of form factors.