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The Bi–Ni binary system has been of interest due to possible unconventional superconductivity aroused therein, such as time-reversal symmetry breaking in Bi/Ni bilayers or the coexistence of superconductivity and ferromagnetism in Bi3Ni crystals. While Ni acts as a ferromagnetic element in such systems, the role of strong spin-orbit coupling element Bi in superconductivity has remained unexplored. In this work, we systematically studied the effects of Bi stoichiometry on the superconductivity of BixNi1–x thin films fabricated via a composition-spread approach. The superconducting phase map of BixNi1–x thin films exhibited a superconducting composition region attributable to the intermetallic Bi3Ni phase with different amount of excess Bi, revealed by synchrotron X-ray diffraction analysis. Interestingly, the mixed phase region with Bi3Ni and Bi showed unusual increase in the superconducting transition temperature and residual resistance ratio as more Bi impurities were included, with the maximum Tc (= 4.2 K) observed at x ≈ 0.79. A correlation analysis of structural, electrical, and magneto-transport characteristics across the composition variation revealed that the unusual superconducting "dome" is due to two competing roles of Bi: impurity scattering and carrier doping. We found that the carrier doping effect is dominant in the mild doping regime (0.74 ≤ x ≤ 0.79), while impurity scattering becomes more pronounced at larger Bi stoichiometry.
Park, J.
, Horn, J.
, Kirsch, D.
, Pant, R.
, Yoon, H.
, Baek, S.
, Sarker, S.
, Mehta, A.
, Zhang, X.
, Lee, S.
, Greene, R.
, Paglione, J.
and Takeuchi, I.
(2024),
Superconducting phase diagram in BixNi1-x thin films: the effects of Bi stoichiometry on superconductivity, Physical Review Materials, [online], https://doi.org/10.1103/PhysRevMaterials.8.074805, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=957647
(Accessed October 9, 2025)