Theory of Nb-Zr Alloy Superconductivity and First Experimental Demonstration for Superconducting Radio-Frequency Cavity Applications

Niobium-zirconium (Nb-Zr) alloy is an old superconductor that is a promising new candidate for superconducting radio-frequency (SRF) cavity applications. Using density-functional and Eliashberg theories, we show that addition of Zr to a Nb surface in small concentrations increases the critical tempe...

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Bibliographic Details
Published in:arXiv.org 2022-08
Main Authors: Sitaraman, Nathan S, Sun, Zeming, Francis, Ben, Hire, Ajinkya C, Oseroff, Thomas, Baraissov, Zhaslan, Arias, Tomás A, Hennig, Richard, Liepe, Matthias U, Muller, David A, Transtrum, Mark K
Format: Article
Language:English
Subjects:
Alloys
Figure of merit
Holes
Intermetallic compounds
Niobium
Radio frequency
Superconductivity
Superheating
Zirconium base alloys
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Summary:Niobium-zirconium (Nb-Zr) alloy is an old superconductor that is a promising new candidate for superconducting radio-frequency (SRF) cavity applications. Using density-functional and Eliashberg theories, we show that addition of Zr to a Nb surface in small concentrations increases the critical temperature \(T_c\) and improves other superconducting properties. Furthermore, we calculate \(T_c\) for Nb-Zr alloys across a broad range of Zr concentrations, showing good agreement with the literature for disordered alloys as well as the potential for significantly higher \(T_c\) in ordered alloys near 75%Nb/25%Zr composition. We provide experimental verification on Nb-Zr alloy samples and SRF sample test cavities prepared with either physical vapor or our novel electrochemical deposition recipes. These samples have the highest measured \(T_c\) of any Nb-Zr superconductor to date and indicate a reduction in BCS resistance compared to the conventional Nb reference sample; they represent the first steps along a new pathway to greatly enhanced SRF performance. Finally, we use Ginzburg-Landau theory to show that the addition of Zr to a Nb surface increases the superheating field \(B_{sh}\), a key figure of merit for SRF which determines the maximum accelerating gradient at which cavities can operate.
ISSN:2331-8422