Ultrasonic Attenuation in the Intermediate State of Tin

We have measured the ultrasonic attenuation in high-purity Sn cylinders in the intermediate state. The laminar intermediate-state structure was set up with a rotating external field. Andreev's theory of sound attenuation in the intermediate state was extended to allow for arbitrary values of ql, the product of sound propagation vector and electron mean free path. It was then possible to determine the size of the normal regions as a function of applied magnetic field from the experimental data. The intermediate-state structure thus determined agreed reasonably well with the Landau model. The analysis suggests, however, that in the intermediate state the attenuation in the high-frequency limit is not increasing linearly with applied field as simple considerations would suggest. The reason for this is not properly understood at the present time.