Resistance and Thermoelectric Measurements of Cold-Worked Copper and the Resistance Minimum at Low Temperatures

Measurements of the change of residual resistance ratio of copper as a function of the percentage reduction in cross-sectional area by cold-working in liquid helium, liquid nitrogen or at room temperature and subsequent ageing treatments show (1) the relative change of the ratio during recovery between 77^∘{}K and room temperature to that accompanying recovery and recrystallization at higher temperatures; (2) that there appears to be no recovery process taking place below 77^∘{}K; (3) that specimens cold-worked in liquid helium or nitrogen and aged at room temperature have a higher residual resistance ratio than specimens both cold-worked and aged at room temperature.We find that the thermoelectric force, E, of copper specimens cold-worked at room temperature or liquid helium is positive relative to annealed copper in the range 4^∘{}-40^∘{}K (taking 4^∘{}K as zero). The measurements are discussed in relation to the origin of the electrical resistance minimum which is found in copper at 10^∘{}-14^∘{}K.