Spin-Triplet Pairing State Evidenced by Half-Quantum Flux in a Noncentrosymmetric Superconductor

Xiaoying Xu, Yufan Li, and C. L. Chien

Phys. Rev. Lett. 124, 167001 – Published 22 April 2020

Abstract

A prime category of superconducting materials in which to look for spin-triplet pairing and topological superconductivity are superconductors without inversion symmetry. It is predicted that the broken parity symmetry gives rise to an admixture of spin-triplet and spin-singlet pairing states. However, experimental confirmation of pairing mixing in any material remains elusive. In this work, we perform a phase-sensitive experiment to examine the pairing state of noncentrosymmetric superconductor $α$ -BiPd. The Little-Parks effect observed in mesoscopic polycrystalline $α$ -BiPd rings reveals the presence of half-integer magnetic flux quantization, which provides a decisive evidence for the spin-triplet pairing state. We find both half-quantum fluxes and integer-quantum fluxes of different proportions, consistent with the scenario of an admixture of singlet-triplet pairing.

Received 23 January 2020
Accepted 1 April 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.167001

Physics Subject Headings (PhySH)

Spin-triplet pairing Topological materials Topological superconductors p-wave

Noncentrosymmetric materials Polycrystalline materials Unconventional superconductors Weak links

Liquid helium cooling Lithography Resistivity measurements Scanning electron microscopy X-ray diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Xiaoying Xu ^1,*, Yufan Li ^1,†, and C. L. Chien ^1,2,‡

¹Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
²Department of Physics, National Taiwan University, Taipei 10617, Taiwan