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TT: Fachverband Tiefe Temperaturen

TT 39: Superconductivity: (General) Theory

TT 39.7: Vortrag

Mittwoch, 22. März 2017, 11:00–11:15, HSZ 103

Inflated nodes in multiband superconductors with broken time-reversal symmetry — •Carsten Timm¹, Daniel F. Agterberg², and Philip M. R. Brydon³ — ¹Institute of Theoretical Physics, Technische Universität Dresden, Germany — ²Department of Physics, University of Wisconsin, Milwaukee, U.S.A. — ³Department of Physics, University of Otago, Dunedin, New Zealand

It is commonly believed that superconductors fall into one of three classes: They can have a full energy gap, a gap with point nodes, or a gap with line nodes. We show that multiband, even-parity, nodal superconducting states that break time-reversal symmetry do not belong to these classes. Instead, they generically possess two-dimensional Fermi surfaces. These Fermi surfaces can be visualized as being generated by “inflating” point and line nodes into spheroids and tori, respectively. The inflated nodes are topologically protected by a Z₂ invariant, which we give in terms of a Pfaffian. We also show that such states can be energetically stable in spite of the extended Fermi surfaces; they form the state with the lowest free energy if spin-orbit coupling is sufficiently strong.