Artificially prepared multilayerd films with periodic and fractal structure, consisting of amorphous superconducting and normal-metal layers have been made by magnetron sputtering. The structure has been confirmed directly by transmission electron micrographs of cross sections of the multilayers. The observed upper parallel critical field of the superconducting transition is related to the layering geometry.

• Received 27 October 1986

DOI:https://doi.org/10.1103/PhysRevB.35.3175