ABSTRACT
We report here the observation of unusual behavior of the temperature dependence of sound velocity in an aluminum single crystal when the sample is in the superconducting state and is subjected to a bias stress. The observed behavior is similar to that found in amorphous materials at low temperatures (T < 1K), where it has been explained in terms of two level tunneling systems (TLS). We interpret our results on aluminum in terms of tunneling of dislocations (kinks) between the two levels (of adjacent potential wells) produced by the bias stress.
The effect of damping on the observed tunneling is to suppress the process by electrons in the normal state.
