Moises Levy
Phys. Dept., Univ. of Wisconsin---Milwaukee, Milwaukee, WI 53201
Surface acoustic wave (SAW) may acoustoelectrically interact with a superconducting film deposited on the surface of the piezoelectric substrate which carries the SAW. The polarization fields accompanying the SAW induce currents in the normal conducting film producing attenuation via Ohmic losses which are subsequently quenched when the film becomes superconducting. In a homogeneous film, the SAW attenuation will be proportional to the resistivity of the film even through the superconducting transition. In a granular film percolation effects broaden both the resistive and attenuation transitions. However, if the number of grains per SAW wavelength is sufficiently small, then the attenuation transition is broadened even more than the resistive transition, and the acoustoelectric attenuation in the normal state is larger than it would be for a homogeneous film with the same sheet resistivity. An acoustoelectric attenuation percolation model has been developed which may yield information about the granularity of the film being measured, or conversely if the granularity is known from other techniques, it is possible then to estimate the resistivity of the individual grains composing the film. In the case of the high T[sub c] film that has been measured, this turns out to be 12.5 (mu)(Omega) cm for grains whose dimensions are about 3000 (Angstrom). [This research was supported by ONR.]