We have measured the perpendicular upper critical magnetic field HC2, the excess conductance σ′ due to superconducting fluctuations and the superconducting transition temperature TC in granular aluminum films in the wide range of the sheet resistance R□, 100Ω≤R□≤15 kΩ. The temperature dependence of HC2 near TC has been analyzed in the form HC2=HC20(1-T/TC)n. For relatively low resistance films, the index n is almost unit. However, n decreases steeply at a characteristic resistance R*≈1.5kΩ and approaches 0.7 with increase of R□. This value of n agrees with that predicted from the percolation theory taking account of the fractal nature of clusters. With increasing R□ beyond R*, the value of σ′ decreases drastically as compared with that estimated from the sum of Aslamazov-Larkin and Maki-Thompson terms. The sheet resistance dependence of σ′ can be explained qualitatively by a model based on the scaling law of percolation. The value of TC decreases gradually.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering