SAW MEASUREMENTS ON A NB FILM AND AN YBA2CU3O7 FILM

Surface acoustic wave attenuation measurements have been performed in a screen room on a superconducting film of Nb at 659 MHz and on a high T(c) film of YBa2Cu3O7 at 168 MHz. The attenuation in the Nb film is due to electron-phonon interaction and follows a BCS curve in the superconducting state. The measured change in attenuation was 0.8 dB/cm giving an electron mean free path which is about twice as large as the value obtained from the sheet resistivity of this Nb film. The sheet resistivity of the YBa2Cu3O7 film was 45 OMEGA/open-square-box, and the observed change in attenuation at T(c) = 87 K was 0.18 dB/cm. A percolation model is proposed for describing the behavior of both the attenuation and the sheet resistivity in the superconducting state. This model is also used to determine the minimum resistance of YBa2Cu3O7 along the ab plane. It is found to be 12.5-mu-OMEGA-cm.