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arXiv · 1705.06383

Superheating in coated niobium

T. Junginger·W. Wasserman·R. E. Laxdal
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Abstract

Using muon spin rotation it is shown that the field of first flux penetration H_entry in Nb is enhanced by about 30% if coated with an overlayer of Nb_3Sn or MgB_2. This is consistent with an increase from the lower critical magnetic field H_c1 up to the superheating field H_sh of the Nb substrate. In the experiments presented here coatings of Nb_3Sn and MgB_2 with a thickness between 50 and 2000nm have been tested. H_entry does not depend on material or thickness. This suggests that the energy barrier at the boundary between the two materials prevents flux entry up to H_sh of the substrate. A mechanism consistent with these findings is that the proximity effect recovers the stability of the energy barrier for flux penetration, which is suppressed by defects for uncoated samples. Additionally, a low temperature baked Nb sample has been tested. Here a 6% increase of H_entry was found, also pushing H_entry beyond H_c1.

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T. Junginger, W. Wasserman, R. E. Laxdal. 2017-05-18. Superheating in coated niobium. https://doi.org/10.1088/1361-6668%2Faa8e3a

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