Comment on "Strong Meissner screening change in superconducting radio frequency cavities due to mild baking" [Appl. Phys. Lett. 104, 072601 (2014)]

Abstract

In a recent Letter by Romanenko et al., the authors used low-energy muon spin rotation (LE-$\mu$SR) to measure the Meissner screening profile in cutouts from Nb superconducting radio frequency (SRF) cavities, systematically comparing how different surface treatments affect the screening properties of the elemental type-II superconductor. They reported a "strong" modification to the character of the screening profile upon mild baking at 120 ${}^{\circ }$C for 48 h, which was interpreted as a depth-dependent carrier mean-free-path resulting from a "gradient in vacancy concentration" near the surface. While this observation led to speculation that this surface treatment yields an "effective" superconducting bilayer, we suggest that its likeness to such is accidental and that the behavior is an artifact from the analysis.

4 pages, 2 figures

References in corpus (4)

• Multilayer coating for higher accelerating fields in superconducting radio-frequency cavities: a review of theoretical aspects
• Depth-resolved measurements of the Meissner screening profile in surface-treated Nb
• High-Field Q-slope Mitigation due to Impurity Profile in Superconducting Radio-Frequency Cavities
• Evidence for current suppression in superconductor-superconductor bilayers

Cited by in corpus (5)

• Measurements of the first-flux-penetration field in surface-treated and coated Nb: Distinguishing between surface pinning and an interface energy barrier
• Depth-resolved Characterization of Meissner Screening Breakdown in Surface Treated Niobium
• Niobium's intrinsic coherence length and penetration depth revisited using low-energy muon spin spectroscopy and secondary-ion mass spectrometry
• Search for inhomogeneous Meissner screening in Nb induced by low-temperature surface treatments
• Implantation studies of low-energy positive muons in niobium thin films