Measurements of the first-flux-penetration field in surface-treated and coated Nb: Distinguishing between surface pinning and an interface energy barrier

Abstract

We report measurements of the first-flux-penetration field in surface-treated and coated Nb samples using muon spin rotation ($\mu$SR). Using thin Ag foils as energy moderators for the implanted muon spin-probes, we "profile" the vortex penetration field ${\mu }_0{H}_{\mathrm{vp}}$ at sub-surface depths on the order of $\sim 10$ $\mu$m to $\sim 100$ $\mu$m. In a coated sample [Nb${}_3$Sn(2 $\mu$m)/Nb], we find that ${\mu }_0{H}_{\mathrm{vp}}$ 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 ${}^{\circ }$C for 48 h], vortex penetration onsets close to pure Nb's lower critical field ${\mu }_0{H}_{c1}\approx 170$ mT, 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 (SRF) cavities, is discussed.

10 pages, 6 figures

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Cited by in corpus (5)

• Impact of border defects on the magnetic flux penetration in superconducting films
• Depth-resolved Characterization of Meissner Screening Breakdown in Surface Treated Niobium
• Search for inhomogeneous Meissner screening in Nb induced by low-temperature surface treatments
• Implantation studies of low-energy positive muons in niobium thin films
• Superconducting properties of thin film $\mathrm{N}{\mathrm{b}}_{1-\mathrm{x}}\mathrm{T}{\mathrm{i}}_{\mathrm{x}}\mathrm{N}$ studied via the NMR of implanted ${}^8$Li