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Condensed Matter Seminar – Daniel Agterberg (Univ. Wisconsin-Milwaukee)
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Topologically protected Bogoliubov Fermi surfaces
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 are topologically protected from being gapped by a non-trivial Z2 invariant. In this talk, I will discuss the physical origin, topological protection, and energetic stability of these Bogoliubov Fermi surfaces, using chiral superconductivity in j=3/2 fermions as a representative example.
Host: Peter Hirschfeld