Anomalous Ultrasonic Attenuation in Pure Superconducting Nb

Pure-state data are presented for ultrasonic attenuation in clean Nb (resistivity ratio ∼ 7000) in the domain $0.4<\mathrm{ql}<\mathrm{}6\mathrm{}$, where $q=\frac{2\pi }{\lambda }$ is the phonon wave vector for phonons of wavelength $\lambda$ and $l$ is the electronic mean free path. These results are presented in light of the models of Fate and Trivisonno, Lacy and Daniel, and Maki. In general, no model is found completely adequate.