Symmetry, nodal structure, and Bogoliubov Fermi surfaces for nonlocal pairing

TL;DR

This paper explores how nonlocal pairing and additional internal degrees of freedom influence the symmetry, nodal structure, and emergence of Bogoliubov Fermi surfaces in centrosymmetric superconductors, expanding the understanding of multiband effects.

Contribution

It extends the analysis of pairing symmetries and nodal structures by including nonlocal pairing and internal degrees of freedom beyond the $j=3/2$ model, revealing a broader range of possible behaviors.

Findings

Nonlocal pairing significantly enlarges the space of possible pairing symmetries.

A simple criterion for nodes based on scalar products of form factors is established.

The analysis provides symmetry-based guidance for understanding Bogoliubov Fermi surfaces.

Abstract

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.