Effects of Superconducting Fluctuations on the Ultrasonic Attenuation in a Thin Aluminum Film

The attenuation of 2-GHz acoustic surface waves in a 300-Å aluminum film has been measured in the temperature region around the superconducting transition temperature. The simple BCS theory yields a gap parameter of 3.60. While microwave electromagnetic-attenuation measurements in the film indicate critical fluctuation effects near $T_c$, there appear to be no such fluctuation effects in the ultrasonic-attenuation data of this short-mean-free-path Al film.