Depth-Resolved Measurements of the Meissner Screening Profile in Surface-Treated Nb

We report depth-resolved measurements of the Meissner screening profile in several surface-treated Nb samples using low-energy muon spin rotation. In these experiments, implanted positive muons, whose stopping depths below Nb's surface are adjusted between approximately 10 nm and 150 nm, reveal the field distribution inside the superconducting element via their spin precession (communicated through their radioactive decay products). We compare how the field screening is modified by different surface treatments commonly used to prepare superconducting radio-frequency cavities used in accelerator beamlines. In contrast to an earlier report [A. Romanenko et al., Appl. Phys. Lett. 104, 072601 (2014)], we find no evidence for any anomalous modifications to the Meissner profiles, with all data being well described by a London model. Differences in screening properties between surface treatments can be explained by changes to the carrier mean free paths resulting from dopant profiles near the material's surface.

Automated summary

We present depth-resolved measurements of the Meissner screening profile in surface-treated Nb samples using low-energy muon spin rotation. We find no evidence for any anomalous modifications to the Meissner profiles, with all data well described by a London model. Differences in screening properties between surface treatments can be explained by changes to the carrier mean free paths resulting from dopant profiles near the material's surface.