Thermal Resistivity at Pb-Cu and Sn-Cu Interfaces between 1.3 and 2.1°K

Measurements have been made of the thermal resistivity at lead-copper and tin-copper interfaces for $1.3\le T\le 2.1°$K. By the application of a magnetic field the lead or the tin could be transformed from the superconducting to the normal state. This permitted measurements of the changes in the thermal resistivity at the interface between two metals produced by allowing one of the metals to become superconducting. The thermal resistivity at an interface formed by vacuum casting lead onto copper was found to be $9.3T^{-3.7\mathrm{}}°$K ${\mathrm{cm}}^2$/W with the lead superconducting. An interface formed by growing a single crystal of lead onto a single crystal of copper had an interface resistivity of $9.3T^{-4.3\mathrm{}}°$K ${\mathrm{cm}}^2$/W with the lead superconducting. Upon application of a magnetic field to make the lead normal, the thermal resistivity at the interface dropped to a value too small to measure reliably, less than 0.04°K ${\mathrm{cm}}^2$/W. These measurements suggest that the heat transfer across Pb-Cu interfaces by electrons is increased considerably by changing the lead from the superconducting to the normal state. The thermal resistivity at the interface between tin and copper, with the tin superconducting, was about $\frac{1}{5}$ as great as that for lead and copper, with the lead superconducting. An alloy zone formed at tin-copper interfaces obscures to some extent the nature of the resistivity at these interfaces. However, heat transfer at Sn-Cu interfaces appears to be dominated by electrons with the tin either superconducting or normal. Heat transfer by electrons at all interfaces behaves qualitatively in a manner similar to the thermal conduction by electrons in the superconductor used. A rod made of alternate layers of Pb and Cu had a much larger thermal resistivity with the lead superconducting than with it normal. This suggests the use of such a sandwich structure as a thermal switch.