Anomalous Ultrasonic Attenuation in Pure Superconducting Nb

Abstract

We have observed anomalous ultrasonic attenuation in pure superconducting Nb[100] for $q{l}_{e}\ensuremath{\approx}1$. The anomalous behavior is believed to be associated with the high purity of the sample, which has a measured resistivity ratio of 6500. The attenuation data have been analyzed by assuming that the material has two energy gaps, one with a standard BCS value of $2\frac{{\ensuremath{\Delta}}_{1}(0)}{k{T}_{c}}=3.4$ and the other with $2\frac{{\ensuremath{\Delta}}_{2}(0)}{k{T}_{c}}=10$.