Signatures of enhanced superconducting properties in niobium cavities
D. Bafia, A. Grassellino, M. Checchin, J. F. Zasadzinski, A. Romanenko
DOI 10.1103/PhysRevApplied.23.054052 · Physical Review Applied
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Abstract
Superconducting radio-frequency (SRF) niobium cavities are critical for modern particle accelerators, as well as for advancing superconducting quantum systems and enabling ultrasensitive searches for new physics. In this work, we report a systematic observation of an anomalous frequency dip in Nb cavities, which occurs at temperatures just below the critical temperature (Tc), indicative of enhanced superconducting properties at T≪Tc. The magnitude of this dip is strongly correlated with the rf surface resistance, impurity distribution near the surface, and Tc. Additionally, we report measurements of the coherence peak in the ac conductivity of two Nb SRF cavities processed using distinct methods. By comparing recent theories developed to model this experimental data, we show that the frequency-dip feature, larger coherence peak height, and reduction in the temperature-dependent surface resistance with rf current occur at minimal but finite levels of disorder.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 9.2 | Pressure not reported | onset |
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