Theory of dislocation tunneling through a pinning point

The ultrasonic attenuation and the sound velocity at 10 MHz were measured in deformed Al single crystals in the temperature range between 1.5 and 50 K. In the high purity specimen (RRR=20000) the change in sound velocity due to deformation shows a step in temperature dependence at 17 K, which corresponds to the 11 K relaxation peak at 50 kHz found by Kosugi and Kino [J. Phys. Soc. Jpn. 58 (1989) 4269], although the change in attenuation due to deformation was masked by the large background attenuation due to phonon–electron interaction. From the present experiment and that of Kosugi and Kino, the activation energy and the attack frequency of the relaxation process are estimated to be 14 meV and 1.0×1012/s, respectively. If the kink pair formation process of dislocations on the Peierls potential is responsible for this relaxation, the Peierls stress is 5.4×10-5G, where G is the shear modulus, and this value does not conflict with the flow stress at low temperatures.