The specific heat of copper at temperatures below 0.2 K

The specific heat of high-purity copper has been measured over the temperature range of 0.03–0.2 K. It is shown that an anomaly appears in the specific heats of some samples. The temperature dependence is ~T ^\s-2 at T \> 0.03 K, and at 0.03 K the magnitude is equal to that of the contribution from conduction electrons. We have not been able to explain the origin of this anomaly.This work was supported in part by the U.S. Department of Energy under contract DE-AC02-76ER01198.