A sharp transition from reversible behaviour to irreversible behaviour in the superconducting mixed slate of single-crystal samples of CeRuz is described. Magnetization, AC susceptibility, resistivity and specific heal measuremenLs under an applied field are reported. The results are discussed in relation to conventional models and those of more novel superconductivity. such as the Fulde-Ferrel stake.

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We have studied the I-V characteristics, the dc resistance at the origin R(T), and the critical current It(T) of arrays consisting of n • n (n = 10, 20, 30, and 40) In squares separated by Au/In regions. The superconducting squares have side ds(In) from 7.5 to 15 tzm and dN(Au/In) from 2.5 to 11 ~m. These devices show two transition temperatures in their R(T) curve; one at Tcc near Tc(In) and another one at T* above Tc(Au/In). The I-V curves for each temperature region resemble recent published results on NbN granular films. These arrays follow a formalism proposed by Wolf, Gubser, and Imry to describe the transition to a resistanceless state at T*. The measured values of I~(T) are larger than expected from n noninteracting Bardeen-Johnson functions in parallel, although the exponential behavior in temperature is followed. They are compatible with the idea of bands in the quasiparticle spectrum in the Au/In regions. Deviations in I~(T) from an exponential behavior in T near T* have been analyzed by applying to SNS arrays ideas developed for phase transitions in SIS arrays. Evidence that at T* we may be observing a phase transition at Tcj due to the Josephson coupling between In squares exists but it needs the development of theoretical work to be put on more solid grounds.

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