Bohm-Jung Yang
I am going to talk about the topological properties of the superconductivity that coexists with stable magnetism. In the first part of this talk, we propose a route to achieve odd-parity spin- triplet superconductivity in metallic collinear antiferromagnets with inversion symmetry. Owing to the existence of hidden antiunitary symmetry, which we call the effective time- reversal symmetry (eTRS), the Fermi surfaces of ordinary antiferromagnetic metals are generally spin-degenerate, and spin-singlet pairing is favored. However, by introducing a local inversion symmetry breaking perturbation that also breaks the eTRS, we can lift the degeneracy to obtain spin-polarized Fermi surfaces. In the weak-coupling limit, the spin- polarized Fermi surfaces constrain the electrons to form spin-triplet Cooper pairs with odd- parity. Furthermore, we find that the odd-parity superconducting states host nontrivial band topologies manifested as chiral topological superconductors, second-order topological superconductors, and nodal superconductors. In the second part, I am going to talk about topological superconductivity of spin-polarized fermions in ferromagnets. By generalizing the Fu-Berg-Sato criterion to account for higher order band topology, we show that doped nodal semimetals of spin-polarized fermions can host various types of magnetic higher-order topological superconductivity.
[1] S. H. Lee and B. -J. Yang, "Odd-parity spin-triplet superconductivity in centrosymmetric antiferromagnetic metals", arxiv:2006.15775[2] J. Ahn and B. –J. Yang, “Higher-order topological superconductivity of spin-polarized fermions”, arXiv:1906.02709; Physical Review Research 2, 012060(R) (2020)