Measurements of the first-flux-penetration field in surface-treated and coated Nb: distinguishing between near-surface pinning and an interface energy barrier
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Bibliographic record
Abstract
Abstract We report measurements of the first-flux-penetration field in surface-treated and coated Nb samples using <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>μ</mml:mi> <mml:mtext>SR</mml:mtext> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> . Using thin Ag foils as energy moderators for the implanted muon spin-probes, we ‘profile’ the vortex penetration field <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>μ</mml:mi> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mi>H</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>vp</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> at sub-surface depths on the order of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>10</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>μ</mml:mtext> </mml:mrow> </mml:math> m to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>100</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>μ</mml:mtext> </mml:mrow> </mml:math> m. In a coated sample [Nb 3 Sn( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mtext>μ</mml:mtext> <mml:mtext>m</mml:mtext> </mml:mrow> </mml:math> )/Nb], we find that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>μ</mml:mi> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mi>H</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>vp</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> is depth-independent with a value of 234.5(35) mT, consistent with Nb’s metastable superheating field and suggestive of surface energy barrier for flux penetration. Conversely, in a surface-treated sample [Nb baked in vacuum at 120 ∘ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:math> for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>48</mml:mn> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mtext>h</mml:mtext> </mml:mrow> </mml:math> ], vortex penetration onsets close to pure Nb’s lower critical field <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>μ</mml:mi> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mi>H</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mrow> <mml:mn>170</mml:mn> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mtext>mT</mml:mtext> </mml:mrow> </mml:math> , but increases with increasing implantation depth, consistent with flux-pinning localized at the surface. The implication of these results for technical applications of superconducting Nb, such as superconducting radio frequency cavities, is discussed.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it