The thermo-electric behaviour of tin and silver at liquid-helium temperatures

Abstract

A new method, employing a superconducting galvanometer and requiring a temperature difference of only 0·01° K between the ends of the specimen, has been used to measure the absolute thermo-electric powers of tin and silver at liquid-helium temperatures. It has been shown that the thermo-electric power of tin vanishes abruptly at the superconducting transition temperature; this observation disagrees with the conclusions of Casimir & Rademakers, who report a curious behaviour above the transition temperature which they hold to ‘foreshadow’ the onset of superconductivity. The thermo-electric behaviour of metals in the normal (non-superconducting) state shows striking disagreement with the predictions of the free-electron theory. Thus, the thermo-electric power does not vary linearly with the absolute temperature, and for silver has a positive, instead of a negative, sign. The thermo-electric power is profoundly influenced by the presence of strains in the specimen, and by very small amounts of impurity, the temperature dependence becoming more nearly linear for impure or highly strained specimens. A marked anisotropy has been found in the thermo-electric behaviour of single crystals of tin.