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Bogoliubov Fermi Surfaces in Superconductors with Broken Time-Reversal Symmetry

D. F. Agterberg, P. M. R. Brydon, and C. Timm
Phys. Rev. Lett. 118, 127001 – Published 24 March 2017
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Abstract

It is commonly believed that, in the absence of disorder or an external magnetic field, there are three possible types of superconducting excitation gaps: The gap is nodeless, it has point nodes, or it has line nodes. Here, we show that, for an even-parity nodal superconducting state which spontaneously breaks time-reversal symmetry, the low-energy excitation spectrum generally does not belong to any of these categories; instead, it has extended Bogoliubov Fermi surfaces. These Fermi surfaces can be visualized as two-dimensional surfaces generated by “inflating” point or line nodes into spheroids or tori, respectively. These inflated nodes are topologically protected from being gapped by a Z2 invariant, which we give in terms of a Pfaffian. We also show that superconducting states possessing these Fermi surfaces can be energetically stable. A crucial ingredient in our theory is that more than one band is involved in the pairing; since all candidate materials for even-parity superconductivity with broken time-reversal symmetry are multiband systems, we expect these Z2-protected Fermi surfaces to be ubiquitous.

  • Figure
  • Received 5 December 2016

DOI:https://doi.org/10.1103/PhysRevLett.118.127001

© 2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

D. F. Agterberg1,*, P. M. R. Brydon2,†, and C. Timm3,‡

  • 1Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53201, USA
  • 2Department of Physics, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
  • 3Institute of Theoretical Physics, Technische Universität Dresden, 01062 Dresden, Germany

  • *agterber@uwm.edu
  • philip.brydon@otago.ac.nz
  • carsten.timm@tu-dresden.de

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Issue

Vol. 118, Iss. 12 — 24 March 2017

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