Abstract
The random Josephson network consisting of small Sn particles with light oxidation on the surface were prepared by repeating the vacuum evaporation and oxidation. The size of the particles was about 300 Å in diameter and the strength of the Josephson coupling was controlled by changing the degree of oxidation. The quasi-reentrant behavior was observed in the samples with a sheet resistance of about 6k Ω, which is close to h/4 e 2. More resistive samples behaved like semiconductors, and less resistive ones like usual superconducting films. The samples annealed in air did not obey the 6 kΩ criterion. In some of these samples the periodic steps and spikes were observed in the current voltage characteristics when the samples were irradiated by microwaves. The observed period was very close to 2 ef where e is the elementary charge and ƒ is the frequency of microwave.
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