The nature of the change in the conditions for surmounting pinning centers by dislocation in lead at the superconducting transition

Abstract

The effect of the presence of Sb on the amplitude dependence of ultrasonic attenuation α in the concentration range 1.7×10⁻³ to 4.25×10⁻¹ at % has been studied systematically on Pb single crystals at 1.4 and 4.2 K (superconducting and normal states) and 77 K. The dependence curve shifts toward greater amplitudesU with increasing concentrationC and to smallerU whenT goes from 1.4 to 4.2 K. The shift toward greaterU at the transition to the normal state is observed for all concentrations. The amplitude-independent attenuation α _i varies with concentration nonmonotonically: IncreasingC causes α _i first to diminish (the minimum atC=0.034 at %) and then to grow. AtC≥0.034at %, α _i does not change at the n-s transition. The studies suggest that the damping factor for dislocations in impure crystals practically does not change at the superconducting transition. Here the damping is essentially due to the dynamic dislocation-impurity interaction. The change in the conditions for a dislocation surmounting the pinning centers at the superconducting transition is determined by the quasistatic mechanism of lowering barriers.