Thermoelectric measurements on tungsten at ultra low temperatures

Measurements are reported of the thermoelectric ratio G for three zone-refined tungsten samples at temperatures down to 45 mK. For the purest sample (Rsub(300K)/Rsub(0K) = 44 000), G behaves simply and in accord with expectations. For two less pure samples (Rsub(300K)/Rsub(0K) = 34 000 and 22 000), G behaves anomalously, becoming increasingly more negative with decreasing temperature down to at least 45 mK. This anomalous behavior is tentatively attributed to trace amounts of iron. (Auth.)