Spin-triplet superconductivity in Weyl nodal-line semimetals

Abstract

Topological semimetals are three dimensional materials with symmetry-protected massless bulk excitations. As a special case, Weyl nodal-line semimetals are realized in materials either having no inversion or broken time-reversal symmetry and feature bulk nodal lines. The 111-family of materials, LaNiSi, LaPtSi and LaPtGe (all lacking inversion symmetry), belong to this class. Here, by combining muon-spin rotation and relaxation with thermodynamic measurements, we find that these materials exhibit a fully-gapped superconducting ground state, while spontaneously breaking time-reversal symmetry at the superconducting transition. Since time-reversal symmetry is essential for protecting the normal-state topology, its breaking upon entering the superconducting state should remarkably result in a topological phase transition. By developing a minimal model for the normal-state band structure and assuming a purely spin-triplet pairing, we show that the superconducting properties across the family can be described accurately. Our results demonstrate that the 111-family reported here provides an ideal test-bed for investigating the rich interplay between the exotic properties of Weyl nodal-line fermions and unconventional superconductivity.

11 pages, 6 figures

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• Nodeless superconductivity in the topological nodal-line semimetal CaSb2
• Signature of point nodal superconductivity in the Dirac semimetal PdTe
• ZrOsSi: A $Z_2$ topological metal with a superconducting ground state
• Nodeless superconductivity in the noncentrosymmetric ThIrSi compound
• Disorder induced dynamical interband response in Dirac nodal line semimetals
• A Family of Lanthanide Noncentrosymmetric Superconductors La${}_4$$TX$ ($T$ = Ru, Rh, Ir; $X$ = Al, In)
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• Higher-order topological superconductivity in type-II time-reversal-symmetric Weyl semimetals with a hybrid pairing
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