We have measured the perpendicular upper critical magnetic field H-C2, the excess conductance sigma ' due to superconducting fluctuations and the superconducting transition temperature Te in granular aluminum films in the wide range of the sheet resistance R-square, 100 Omega less than or equal to R-square less than or equal to 15 k Omega. The temperature dependence of H-C2 near T-C has been analyzed in the form H-C2 = H-C2(0)(1 - T/T-C)(n). For relatively low resistance films, the index n is almost unit. However, n decreases steeply at a characteristic resistance R degrees approximate to 1.5 k Omega and approaches 0.7 with increase of R-square. This value of n agrees with that predicted from the percolation theory taking account of the fractal nature of clusters. With increasing R-square beyond R*, the value of sigma ' decreases drastically as compared with that estimated from the sum of Aslamazov-Larkin and Maki-Thompson terms. The sheet resistance dependence of sigma ' can be explained qualitatively by a model based on the scaling law of percolation. The value of T-C decreases gradually. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 22]
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