Dc and ac Josephson effects in a granular material

This paper reports on three-dimensional systems of point contacts that were prepared by pressing together Niobium grains of about 100 μm diameter inside a sapphire cylinder. Current-voltage characteristics were studied in dependence of temperature and, in addition, of the power of incident microwaves (X-bank). The results are similar to those established for a single weak link junction. Only for small currents the sample showed different behavior. The inverse a.c. Josephson effect was observed. The measured d.c. voltage shows and alternating temperature dependence which might be expected following the calculations of J.J. Chang for a weak link of small capacity and small resistance