Abstract
The maximum zero-voltage tunnel current I0and its fluctuations were measured for Josephson tunnel junctions as a function of the normal state resistanceRin the range of 50-300 Ω atT = 4.2K. The junctions, based on pure lead, have areas of about 100 µm2, corresponding to capacitancesCof about 3 pF. The results obtained from a simple noise model, describing the junction in the zero-voltage state as a parallel resonant circuit with parametersC, L \sim \Phi_{0}/2\piI_{0S}, andR, are in good agreement with the experiments. It is shown that the deviation of the experimental results for high-resistivity junctions from the theory of Ambegaokar and Baratoff is due to thermal noise currents originating in the normal state resistanceR.

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