Calculation of quantum tunneling for a spatially extended defect: The dislocation kink in copper has a low effective mass

Several experiments indicate that there are atomic tunneling defects in pla stically deformed metals. How this is possible has not been clear, given th e large mass of the metal atoms. Using a classical molecular-dynamics calcu lation, we determine the structures, energy barriers, effective masses, and quantum tunneling rates fur dislocation kinks and jogs in copper screw dis locations. We find that jugs are unlikely to tunnel, but the kinks should h ave large quantum fluctuations. The kink motion involves hundreds of atoms each shifting a tiny amount, leading to a small effective mass and tunnelin g barrier.