Observation of half-quantum flux in topological superconductor β-Bi₂Pd

Magnetic flux quantization is one of the defining characteristics of a superconductor. We report the observation of half-integer magnetic flux quantization in mesoscopic rings of superconducting β-Bi₂Pd thin films [1]. The half-quantum fluxoid (HQF) manifests itself as a phase shift in the quantum oscillations of the superconducting critical temperature. The superconducting ring energetically prefers half flux quanta with fractional quantum numbers of 1/2, 3/2, 5/2, etc., instead of usual integer numbers of 0, 1, 2, etc. This result is consistent with β-Bi₂Pd having a spin-triplet pairing symmetry, which may be expected from β-Bi₂Pd as a topological supercondcutor [2,3]. Our findings usher in a new paradigm for identifying spin-triplet pairing, and new venues for studying topological superconductivity.


[1] Y. Li et al., Science 366, 238-241 (2019).
[2] M. Sakano, et al., Nature Communications 6, 8595 (2015).
[3] K. Iwaya, et al., Nature Communications 8, 976 (2017).