Search for inhomogeneous Meissner screening in Nb induced by low-temperature surface treatments
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arXiv
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2024
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| author | McFadden, Ryan M. L. Junginger, Tobias |
| author_facet | McFadden, Ryan M. L. Junginger, Tobias |
| contents | Empirical surface treatments, such as low-temperature baking (LTB) in a gaseous atmosphere or in vacuum, are important for the surface preparation of Nb superconducting radio frequency (SRF) cavities. These treatments inhomogeneously dope the first $\sim$50 nm of Nb's subsurface and are expected to impart depth-dependent characteristics to its Meissner response; however, direct evidence supporting this remains elusive, suggesting the effect is subtle. In this work, we revisit the Meissner profile data for several LTB treatments obtained from low-energy muon spin rotation (LE-$μ$SR) experiments [A. Romanenko et al., Appl. Phys. Lett. 104, 072601 (2014) and R. M. L. McFadden et al., Phys. Rev. Appl. 19, 044018 (2023)], and search for signatures of inhomogeneous field screening. Using a generalized London expression with a recently proposed empirical model for a depth-dependent magnetic penetration depth $λ(z)$, we obtain improved fits to the Meissner data, revealing that the presence of a non-superconducting surface "dead layer" $d \geq 25$ nm is a strong indicator of a reduced supercurrent density at shallow subsurface depths. Our analysis supports the notion that vacuum annealing at 120 $^{\circ}$C for 48 h induces a depth-dependent Meissner response, which has consequences for Nb's ability to maintain a magnetic-flux-free state. Evidence of similar behavior from a "nitrogen infusion" treatment is less compelling. Suggestions for further investigation into the matter are provided. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2405_14615 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Search for inhomogeneous Meissner screening in Nb induced by low-temperature surface treatments McFadden, Ryan M. L. Junginger, Tobias Superconductivity Materials Science Empirical surface treatments, such as low-temperature baking (LTB) in a gaseous atmosphere or in vacuum, are important for the surface preparation of Nb superconducting radio frequency (SRF) cavities. These treatments inhomogeneously dope the first $\sim$50 nm of Nb's subsurface and are expected to impart depth-dependent characteristics to its Meissner response; however, direct evidence supporting this remains elusive, suggesting the effect is subtle. In this work, we revisit the Meissner profile data for several LTB treatments obtained from low-energy muon spin rotation (LE-$μ$SR) experiments [A. Romanenko et al., Appl. Phys. Lett. 104, 072601 (2014) and R. M. L. McFadden et al., Phys. Rev. Appl. 19, 044018 (2023)], and search for signatures of inhomogeneous field screening. Using a generalized London expression with a recently proposed empirical model for a depth-dependent magnetic penetration depth $λ(z)$, we obtain improved fits to the Meissner data, revealing that the presence of a non-superconducting surface "dead layer" $d \geq 25$ nm is a strong indicator of a reduced supercurrent density at shallow subsurface depths. Our analysis supports the notion that vacuum annealing at 120 $^{\circ}$C for 48 h induces a depth-dependent Meissner response, which has consequences for Nb's ability to maintain a magnetic-flux-free state. Evidence of similar behavior from a "nitrogen infusion" treatment is less compelling. Suggestions for further investigation into the matter are provided. |
| title | Search for inhomogeneous Meissner screening in Nb induced by low-temperature surface treatments |
| topic | Superconductivity Materials Science |
| url | https://arxiv.org/abs/2405.14615 |