Bogoliubov Fermi surfaces: General theory, magnetic order, and topology

Abstract

The authors present a general theory for Fermi surfaces of Bogoliubov quasiparticles in superconductors with broken time-reversal symmetry. These Fermi surfaces form two-dimensional nodes of the superconducting gap, which are unique to pairing states with a ``nonunitary'' structure. This generates a nonsuperconducting magnetic order intertwined with superconductivity, which is responsible for inflating the expected zero- or one-dimensional nodes into Bogoliubov Fermi surfaces. Such Fermi surfaces should be present in a large class of superconductors that break time-reversal symmetry.