Topological Superconductivity in Multifold Fermion Metals

Abstract

Recently, multifold fermions characterized by band crossings with multifold degeneracy and Fermi surfaces with nontrivial Chern numbers have been discovered experimentally in AlPt[arXiv:1812.03310] and XSi(X=Rh,Co)[arXiv:1812.04466][arXiv:1901.03358][arXiv:1809.01312]. In this work, we largely expand the family of multifold fermion materials by pointing out that several well-studied noncentrosymmetric superconductors are indeed multifold fermion metals. Importantly, their normal state topological properties, which have been ignored in previous studies, play an important role in the superconducting properties. Taking Li${}_2$Pd${}_3$B and Li${}_2$Pt${}_3$B as examples, we found a large number of unconventional degenerate points, such as double spin-1, spin-3/2, Weyl and double Weyl topological band crossing points near the Fermi energy, which result in finite Chern numbers on Fermi surfaces. Long Fermi arc states in Li${}_2$Pd${}_3$B, originating from the nontrivial band topology were found. Importantly, it has been shown experimentally that Li${}_2$Pd${}_3$B and Li${}_2$Pt${}_3$B are fully gapped and gapless superconductors, respectively. By analyzing the possible pairing symmetries, we suggest that Li${}_2$Pd${}_3$B can be a DIII class topological superconductor with Majorana surface states, even though the spin-orbit coupling in Li${}_2$Pd${}_3$B is negligible. Interestingly, Li${}_2$Pt${}_3$B, being gapless, is likely to be a nodal topological superconductor with dispersionless surface Majorana modes. We further identified that several noncentrosymmetric superconductors, such as Mo${}_3$Al${}_2$C, PdBiSe, Y${}_2$C${}_3$ and La${}_2$C${}_3$, are multifold fermion superconductors whose normal state topological properties have been ignored in previous experimental and theoretical studies.

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Cited by in corpus (6)

• Dirac surface states, multiorbital dimerization and superconductivity in Nb- and Ta-based A15 compounds
• Nonlinear optical responses in multi-orbital topological superconductors
• Nature of the mixed-parity pairing of attractive fermions with spin-orbit coupling in optical lattice
• Band Curvature Effects on Quantum Transport of Spin-1 Chiral Fermion Systems
• Winding Topology of Multifold Exceptional Points
• Discovery of nodal-line superconductivity in chiral crystals