Effect of strain content on the ultrasonic attenuation in the intermediate state of type I superconductors

The attenuation of longitudinal ultrasonic waves has been measured in single-crystal indium doped with 0.002 at. % of bismuth in various physical states of the specimen in the intermediate state over the frequency range 23 to 30 MHz. Two phases have been identified in the superconducting layers. The fundamental frequency v0 for one phase is approximately constant for various physical states of the specimen for the same field, but increases with increase in magnetic field from .07H/sub c/ to 0.9H/sub c/; the fundamental frequency v0 for the other phase decreases with decrease in dislocation density. The origin of the first phase is due to the laminar structure of the intermediate state. The second phase is due to the formation of microstructure in the superconducting layers due to the impurity and strain content in the specimen. The thickness of the microstructure has been calculated utilizing Granato and Lucke's vibrating string model of dislocation for various physical states of the specimen