Combinatorial exploration of the superconducting properties of Bi_xNi_1-x thin films

Strong spin-orbit coupling, multivalency, and the semi-metallic nature of Bi allow for a variety of unusual superconducting phenomena in elemental and compounds of Bi, such as amorphous, high-pressure, high-temperature, and topological superconductivity^1–3. Recently, possible signatures of unconventional p-wave superconductivity in Bi/Ni bilayers have been reported^2,3. However, spontaneous formation of the s-wave phase (Bi₃Ni) has been observed at the Bi/Ni interface, possibly suggesting the p-wave superconductivity due to the proximity effect in the Bi layer rather than through an intrinsic mechanism^4,5. This makes it necessary to further investigate the role of Bi in the superconductivity of the Bi–Ni binary system. In this work, we systematically studied the superconducting properties of Bi_xNi_1-x thin films via a combinatorial approach. The superconducting phase diagram reveals that additional Bi inclusion in Bi₃Ni enhances the critical temperature, with improved coherence length and residual resistance ratio. Remarkably, the bulk superconductivity remains stable even in the excessively Bi-rich region despite low critical current density, implying proximity-induced superconductivity in Bi. Our work provides insights into unusual superconductivity in Bi compounds.

[1] Schindler, Nat. Phys. 14, 918 (2018)

[2] Gong, Sci. Adv. 3, e1602579 (2017)

[3] Chauhan, Phys. Rev. Lett. 122, 017002 (2019)

[4] Chao, Phys. Rev. B 99, 064504 (2019)

[5] Vaughan, Phys. Rev. Res. 2, 013270 (2020)