Year: 2026
Type: preprint
Abstract: Although Cooper pairs in superconductors generally condense into a spin-singlet state, spin-triplet superconductivity has attracted sustained interest since it enables dissipationless spin transport and is an important requirement for manifold topological quantum technologies. Noncentrosymmetric superconductors provide a promising route to triplet pairing because their intrinsic 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 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. Orientation-resolved low-temperature scanning tunneling spectroscopy reveals a strongly anisotropic quasiparticle density of states. 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 provide a momentum-resolved determination of a mixed-parity superconducting order parameter and demonstrate that ASOC alone can foster a substantial spin-triplet component. More broadly, they establish orientation-resolved tunneling 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.
Source: arXiv (Cornell University)
Institutions: University of Konstanz, TU Wien, University of Warwick
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7163512037