Precise measurements of the electrical resistivity of pure copper samples have disclosed two discontinuities in the temperature dependence of the resistivity. They occur at approximately 6.7 K and near 12.1 K. The second is associated with impurity effects whereas the first appears to be a characteristic of the metal itself. It is similar to the discontinuity previously observed in the temperature dependence of the electrical resistivity of Ag by Kos and independently by Ehrlich and Schriempf and attributed by the former to one-step umklapp processes.

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