Angle-resolved phase-sensitive measurement of the anisotropic gap structure in a topological superconductor β-Bi₂Pd

The phase-sensitive experiments provide a powerful probe to resolve the anisotropic gap structures of unconventional superconductors^[1]. Notably, an angle-resolved phase-sensitive study definitively established the  pairing symmetry of the high-TC cuprates^[2]. We have recently employed the phase-sensitive experiment to demonstrate the odd-parity pairing symmetry in topological superconductor candidate β-Bi₂Pd. It confirms an anisotropic gap function of β-Bi₂Pd that reverses sign upon the inversion of momentum, i.e., Δ_k=-Δ_-k, consistent with the spin-triplet p-wave pairing state^[3]. To gain further insight into the unconventional gap symmetry of β-Bi₂Pd, we have carried out an angle-resolved phase-sensitive experiment by systematically varying the crystalline orientations at the β-Bi₂Pd/Nb junctions within the composite ring device. Our preliminary results show that no composite-ring device of crystalline angle smaller than 90° hosts half quantum flux. More interestingly, non-zero phase shifts emerged in Josephson current-phase relation, indicating the possible angle-dependent phase difference.

[1] V. B. Geshkenbein, A. I. Larkin, and A. Barone, Phys. Rev. B 36, 235 (1987). 

[2] J. R. Kirtley et al., Nature Physics 2, 190 (2006).

[3] X. Xu, Y. Li, and C. L. Chien, Phys. Rev. Lett. 132, 056001 (2024).