Voltage Oscillations in Percolating Superconducting Films

We have studied the superconducting transition in thin films of Pb and Al as a function of temperature and magnetic field. Examination of the films in a transmission electron microscope shows a percolative structure with typical small loop sizes of a few thousand angstroms in Pb and a few hundred in Al. We have observed an antisymmetric voltage across the samples as a function of an external DC magnetic field. This voltage shows sharp oscillations with a periodicity of about 250 gauss in Pb and about 1000 gauss in Al. These fields correspond to about one flux quantum in elementary loops of the respective films.