SFB Colloquium

Conventionally, we think of Fermi surfaces as being a hallmark of normal metals, whereas superconductors have a gap towards quasiparticle excitations. In this talk, I point out that not only can superconductors have Fermi surfaces but these appear generically in a certain class of materials. The states at these Fermi surfaces describe Bogoliubov quasiparticles, i.e., superpositions of electrons and holes. The Bogoliubov Fermi surfaces appear for centrosymmetric multiband superconductors that spontaneously break time-reversal symmetry. I discuss topological invariants associated with these Fermi surfaces. Moreover, I show that they can be understood in terms of a pseudomagnetic field generated by interband pairing, which inflates point or line nodes of the gap into surfaces. Finally, I discuss their experimental signatures in the specific heat, magnetic penetration depth, and NMR relaxation rate.