Abstract. Granular films prepared from well-defined In clusters embedded in Kr ( = 10-40 at ?la Kr) show sharp resistance anomalies very close to the superconducting transition temperature. The observed resistance peak(s), which go(es) above the normal state resistance R , and which can be as high as = 1.5 R,, can be explained by a "mesoscopic" effect: Superconducting percolation aggregates of size tP, larger than the superconducting coherence length ts, but smaller than the quasiparticle relaxation length AQ,, have a superconducting gap, but are not yet able to carry a supercurrent.Keywords: Granular superconductors; Nonequilibrium superconductivity; Metal clusters.The superconducting properties of granular metals built from metal clusters embedded in an insulating matrix have been the subjet of both experimental and theoretical work for many years [I]. The discovery of the high-T, oxides with their original granular structure renewed and intensified the interest in this field. One of the suprising features of granular metals is the observation of a metal cluster size dependence of the superconducting transition temperature T,, which is usually higher than that of the bulk material and which increases with decreasing metal cluster size L [2, 31. A consequence of this is that granular metals with a metal cluster size distribution P(L) will have a distribution P( T,) in the superconducting transition temperature, if the clusters are not too strongly coupled as it is the case for metal volume fractions uM < 1. Such a distribution P (T,) will not only result in a broadened transition, but it may also lead to non-equilibrium superconducting phenomena connected with the occurrence of normal conductor (N)-superconductor (S) interfaces. Just below the highest superconducting transition temperature (T,)max, usually that of the smallest clusters, these interfaces occur on a length scale which is given by the cluster size L. This length is much smaller than other characteristic length scales, i. e. the superconducting coherence length ts, or the charge imbalance relaxation length A,, connected with the quasiparticle diffusion from the N-into the S-state. The study of non-equilibrium phenomena on such a "mesoscopic" length scale is of special interest.Non-equilibrium phenomena at N-S interfaces usually show up in the resistance curve R (7') just below T, [4]. For this reason we have studied the superconducting transition in granular In films by resistance measurements very close to T,. These granular films were built from In clusters with different cluster size distributions P ( L ) . In clusters have a L-dependent T, with T, 2 : 4.1 K for L L 5 nm and T, = 3.7 K for L 2 6 nm (51. The resistance curves R ( T ) of such films measured by standard four terminal dc-method
