Nodal superconductivity with spin-triplet component in a noncentrosymmetric weakly-correlated metal

Marcel Strohmeier; Andriy Smolyanyuk; Karsten Held; Michael Smidman; Geetha Balakrishnan; Wolfgang Belzig; Elke Scheer; Angelo Di Bernardo

arXiv · 2606.04742

Nodal superconductivity with spin-triplet component in a noncentrosymmetric weakly-correlated metal

Marcel Strohmeier·Andriy Smolyanyuk·Karsten Held·Michael Smidman·Geetha Balakrishnan·Wolfgang Belzig·Elke Scheer·Angelo Di Bernardo

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Abstract

Although Cooper pairs in superconductors generally condense into a spin-singlet state, spin-triplet superconductivity has attracted sustained interest for dissipationless spin transport and topological quantum technologies. Noncentrosymmetric superconductors provide a promising route to triplet pairing because antisymmetric spin-orbit coupling (ASOC) can mix spin-singlet and spin-triplet states. To date, the strongest evidence for such mixed-parity superconductivity has been reported in heavy-fermion systems, where strong electronic correlations obscure the role of ASOC. Whether ASOC alone can support a substantial spin-triplet component therefore remains unresolved. Here we show that the weakly-correlated noncentrosymmetric superconductor Nb$_{18}$Re$_{82}$ (Nb-Re) hosts a mixed-parity superconducting state with a substantial spin-triplet contribution. Low-temperature scanning tunnelling spectroscopy on single crystals with different crystallographic orientations reveals distinct superconducting spectra. A symmetry-constrained analysis shows that the spectroscopic dataset is explained by an order parameter combining a nodal spin-singlet component with a spin-triplet contribution reaching up to half of the singlet amplitude. These findings resolve the debated pairing symmetry of Nb-Re and demonstrate that ASOC alone can foster triplet pairing. More broadly, they establish orientation-resolved tunnelling spectroscopy as a route to identifying mixed-parity superconducting states and suggest that triplet superconductivity may be more widespread among noncentrosymmetric materials than previously recognized.

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Marcel Strohmeier, Andriy Smolyanyuk, Karsten Held, Michael Smidman, Geetha Balakrishnan, Wolfgang Belzig, Elke Scheer, Angelo Di Bernardo. 2026-06-03. Nodal superconductivity with spin-triplet component in a noncentrosymmetric weakly-correlated metal. https://arxiv.org/abs/2606.04742

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