Superconducting phase diagram in Bi\(_x\)Ni\(_{1-x}\) thin films\(\colon\) the effects of Bi stoichiometry on superconductivity

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 Bi\(_3\)Ni crystals. While Ni acts as a ferromagnetic element i...

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Published in:arXiv.org 2024-06
Main Authors: Park, Jihun, Horn, Jarryd A, Kirsch, Dylan J, Pant, Rohit K, Yoon, Hyeok, Baek, Sungha, Sarker, Suchismita, Mehta, Apurva, Zhang, Xiaohang, Lee, Seunghun, Greene, Richard, Paglione, Johnpierre, Takeuchi, Ichiro
Format: Article
Language:English
Subjects:
Bilayers
Broken symmetry
Composition
Correlation analysis
Doping
Ferromagnetism
Impurities
Phase diagrams
Scattering
Stoichiometry
Superconductivity
Synchrotron radiation
Thin films
Transition temperature
Transport properties
Unconventional superconductivity
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Summary: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 Bi\(_3\)Ni 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 Bi\(_x\)Ni\(_{1-x}\) thin films (\({x} \approx\) 0.5 to 0.9) fabricated via a composition-spread approach. The superconducting phase map of Bi\(_x\)Ni\(_{1-x}\) thin films exhibited a superconducting composition region attributable to the intermetallic Bi\(_3\)Ni phase with different amount of excess Bi, revealed by synchrotron X-ray diffraction analysis. Interestingly, the mixed phase region with Bi\(_3\)Ni and Bi showed unusual increases in the superconducting transition temperature and residual resistance ratio as more Bi impurities were included, with the maximum \({T}_{c}\) (\(=\) 4.2 K) observed at \(x \approx\) 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\(\colon\) impurity scattering and carrier doping. We found that the carrier doping effect is dominant in the mild doping regime (0.74 \(\leq {x} \leq\) 0.79), while impurity scattering becomes more pronounced at larger Bi stoichiometry.
ISSN:2331-8422