Superconducting properties of commercially available solders for low-field applications

Solders with superconducting transitions around 4K are useful in low magnetic field environments for AC current leads or in electrical and mechanical bonds. Accurate knowledge of these solders' superconducting properties is needed for improving high precision experiments. We have measured the electrical resistance of five commercially-available eutectic or near-eutectic solders: 50 %Sn-50 %Pb, 60 %Sn-40 %Pb, 60 %Sn-40 %Pb-0.3 %Sb, 52 %In-48 %Sn, and 96.5 %Sn-3.5 %Ag, down to 2.3 K and in applied magnetic fields from 0 to 0.1 T. We report critical temperatures Tc(B), 90 %-to-10 % transition widths ΔTc, and zero-temperature critical fields Bc₀. Our best candidate for low-loss AC current wiring in low fields is 50 %Sn-50 %Pb, which has a zero-field Tc,₀ = 7.1 K (with ΔTc = 0.6 K), and remained high at Tc (0.1 T) = 6.9K (ΔTc = 0.6 K). We also report, for the first time, Tc and Bc of 60 %Sn-40 %Pb-0.3 %Sb and Bc₀ of 96.5 %Sn-3.5 %Ag. Our Tc,₀ = 3.31 K (ΔTc = 0.08K) for 96.5 %Sn-3.5 %Ag disagrees with a widely adopted value.

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

K.K.H. Leung, B. W. Filippone, C. M. Swank report that financial support was provided by National Science Foundation. K.K.H. Leung, C. Hickman, R. Golub, P. R. Huffman, E. Korobkina report that financial support was provided by US Department of Energy. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.