Ultrasonic attenuation of longitudinal and shear waves in the normal and superconducting states of niobium

Ultrasonic attenuation measurements of both longitudinal and shear waves in the normal and superconducting states were made on niobium single crystals. Frequencies between 50 and 450 M H z were employed. Independent of the mode, frequency, and crystal studied, a deviation of the attenuation ratio _s/_n from BCS behavior was observed. The dependence of _s/_n on frequency and crystal purity are interpreted in terms of a model which assumes a difference in electron mean-free path due to phonon scattering in the normal and superconducting states.Research sponsored in part by NASA Grant 36-006-003 and by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under ASOSR Grant No. 68-1479B.