Comparative study of electron--phonon interaction in three vanadium samples of varying purity. Interim report1 October 1973--30 September 1975

The ultrasonic attenuation coefficient has been measured in the mixed state of three samples of single crystal vanadium of varying purity in order to determine the effect of impurities on theelectron--phonon interaction in the mixed state of vanadium. The resistivity ratio of the three samples was 8, 245, and 400. Within experimental error the superconducting energy gap of the three samples was 3.5 kTc. The electron mean free path determined ultrasonically was 0.4, 2.1 and 0.0004 cm, respectively. A recent theory is presented which indicates that electron--phonon interaction is a strong function of the electron mean free path in the mixed state. The relative attenuation decreases more rapidly for the purer samples as the magnetic field is decreased from the upper critical field, and therefore, the electron--phonon interaction term also decreases more rapidly. There appears to be good quantitative agreement between the experimental results and the theoretical predictions.