Thermal Conductivity of Polycrystalline Zinc below 1°K

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Abstract
Measurements of the thermal conductivity of samples of polycrystalline zinc of thickness 0.1 mm have been carried out between 0.12 and 0.9°K in the normal as well as in the superconducting state to investigate the usefulness of zinc as a thermal switch. The conductivity in the normal state shows a linear dependence on temperature. In the superconducting state it shows a behavior typical of electronic conductivity down to the lowest temperature measured. By applying a magnetic field between 40 and 5000 Oe, magnetoresistivity was also investigated and a strong dependence of thermal conductivity on field was found. Electrical resistivity measurements were performed in magnetic fields at liquid 4He temperatures. The resistivity was found to be independent of temperature for fields up to 9000 Oe. The effect of solder joints using Cd, Sn, In, Zn, and Wood's metal was also investigated, Cd giving the least resistance. The measurements show that zinc should be a useful thermal switch for temperatures below 0.1 and 0.2°K, though effect of a magnetic field on the normal conductivity must be carefully considered.

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