Microwave acoustic studies of the superconducting transition in aluminium

Measurements of the absorption of high frequency longitudinal phonons in the superconducting and intermediate states of aluminium are reported. From the position and the width of the absorption edge that occurs when pair breaking ceases to be effective, the energy gap and its anisotropy can be determined. The variation of tha attenuation coefficient in the intermediate state reveals non-local effects when the electron mean free path is greater than the lamina thickness. (author)