Measurement of Dislocation Tunneling Through a Pinning Atom

Abstract
We find convincing evidence of dislocation tunneling in the superconducting state of an aluminum crystal below 1 K, that is, a flattening of the temperature dependence of applied stress amplitude between 0.1 - 0.5 K for constant decrement of amplitude dependent internal friction (ADIF). Since the interaction potential of a dislocation with an impurity atom has been measured quantitatively by the ADIF, the height ΔU and width Δx of the potential barrier is given as a function of applied stress. For the crossover temperature T* between quantum tunneling and classical thermal activation given as T*= [MATH], thus the only adjusting parameter is an effective mass (M) of the dislocation segment that participates in the tunneling process. Using a modified Cottrell potential which has been determined as the interaction potential, T* is predicted to be 0.7 K when M is taken to be 100 Al atomic masses. This magnitude is consistent with the experimental results.