Size effects in electrical behavior of high-Tc thin-film bridges

The size effects in electrical characteristics of polycrystalline YBa₂Cu₃O_7-x thin-film bridges were studied in the temperature range 4-300 K. It is shown that at T>T_c the decrease of bridge widths w from 200 to 10 μm leads to an increase of resistance R_□ of several times and to a change in R_□ (T) behavior from a metallic type to an activation type. At T<T_c the R_□ (w ) values exponentially increased from the width w was decreased under some definite size L₀. At T<T_c the index α in the temperature dependence of critical current I_c(T )~(T_c-T)^α changed from 3 to 1 if bridge width was decreased. Experimental data are discussed within the framework of the model which takes into account large-scale percolation processes in the system of different intergrain Josephson junctions, where characteristic length L₀ of critical subnetwork is much larger than the grain size