Proximity effect in Ag-Pb alloys

[摘要] The superconducting properties and the microstructure of theAg_100-xPb_x alloys, 1 ≤ x ≤ 5, prepared by rapid quenching from theliquid state with and without subsequent heat treatments, have beenstudied. The x-ray diffraction measurements show that supersaturatedsolid solutions of Pb in Ag can be obtained up to 3.2 at.% Pb ascompared to less than 0.1 at.% Pb at equilibrium. It was found thatby suitable heat treatment it is possible to vary the size and distributionof the Pb precipitates in the Ag matrix and reproducible superconductingproperties in the alloy can be observed. The superconductingtransition temperature of these samples can be qualitatively explainedby the Silvert and Singh's theoretical calculation. The theorydeveloped for the case of layer structure can be extended to three dimensionsto explain the critical current versus temperature behavior.The critical current versus field behavior of these alloys can be explainedby the modification of the Josephson effect. Combining theseresults together with the critical magnetic field measurements and themicrostructure studies of the alloys, it can be concluded that thethree-dimensional proximity effect is the main mechanism for the superconductivityin the Ag-Pb alloys. Based on the Hilsch empiricalformula which was based on experimental results obtained on layerstructures, the experimental data in this investigation show that theelectron-phonon-electron interaction in silver is attractive. The interactionparameter NV obtained is approximately 0.06, which would leadto a value of 10^-5 °K for the superconducting transition temperature ofAg. These values are in agreement with other determinations whichwere done on vapor-deposited metallic film sandwiches. Hence, theHilsch empirical relation valid for layer structures is also valid in thethree-dimensional case. Because the transition temperature and thecritical current can be varied in a wide range by controlling the heattreatments, the Ag-Pb superconductors might have some useful applications.

[发布机构] University:California Institute of Technology;Department:Engineering and Applied Science

[关键词] Applied Physics