Signatures of Enhanced Superconducting Properties in Niobium Cavities

• URL: http://arxiv.org/abs/2103.10601v3
• Date: Wed, 15 Jan 2025 04:12:59 GMT
• Title: Signatures of Enhanced Superconducting Properties in Niobium Cavities
• Authors: D. Bafia, A. Grassellino, M. Checchin, J. F. Zasadzinski, A. Romanenko,
• Abstract summary: We report an anomalous frequency dip in Nb cavities, indicative of enhanced superconducting properties at $T ll T_c$. We also present the first demonstration of the coherence peak in the AC conductivity of Nb SRF cavities.
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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 ultra-sensitive 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 ($T_\mathrm{c}$), indicative of enhanced superconducting properties at $T \ll T_c$. The magnitude of this dip is strongly correlated with the RF surface resistance, impurity distribution near the surface, and $T_\mathrm{c}$. We also present the first demonstration of the coherence peak in the AC conductivity of Nb SRF cavities. 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.

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