Superconducting characteristics of thin tin films in contact with copper films

Abstract

Copper films of calculated thicknesses between 200 and 500° have been evaporated on tin films about 1000 and 2000° thick and the superconducting properties studied. In every case, the critical current for the coated specimen was reduced substantially from the value for an identical tin specimen without copper. In general, the critical current rises relatively slowly as the temperature is decreased. However, at temperatures around 3.0°K and just below 2.3°K, the critical current increases relatively sharply with reduction of temperature. For the thinnest copper coatings, there was no reduction of critical temperature, possibly because the copper film may not have been continuous. For the thicker coatings, the critical temperature of the specimens decreased monotonically with the thickness of the copper. The critical temperatures of the specimens as a function of reduced effective thickness of copper are approximated quite well by the formula