Signatures of Enhanced Superconducting Properties in Niobium Cavities

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 $T_{\mathrm{c}}$. 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.

8 pages, 5 figures, 2 tables

References in corpus (8)

• Proximity breakdown of hydrides in superconducting niobium cavities
• Reduction of Dissipative Nonlinear Conductivity of Superconductors by Static and Microwave Magnetic Fields
• Probing ALPs and the Axiverse with Superconducting Radiofrequency Cavities
• Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor and depairing current density
• Niobium in clean limit: an intrinsic type-I superconductor
• Effects of anisotropy and disorder on the superconducting properties of Niobium
• Oxygen Vacancies in Niobium Pentoxide as a Source of Two-Level System Losses in Superconducting Niobium
• Electromagnetic Response of Disordered Superconducting Cavities

Cited by in corpus (1)

• Local Limit Disorder Characteristics of Superconducting Radio Frequency Cavities