Longitudinal ultrasonic attenuation in normal and superconducting lead at low temperatures

We have measured longitudinal ultrasonic attenuation along the 110] direction in normal and superconducting states in two single crystals of lead, one made from high-purity lead and the other made with high-purity lead doped with 0.1 at % gold. In both specimens an amplitude-dependent effect in the superconducting state has been observed. The data have been taken in the frequency range from 12 to 108 MHz. In high-purity lead the amplitude-independent ratio α_s/α_n shows the frequency dependence observed by Randorff and Marshall, whereas in the doped specimen this ratio shows a very small spread with frequency. In both specimens deformation does not change the α_s/α_n ratio appreciably.