Applicability of the theory based on Andreev reflection to the description of experimental current–voltage characteristics of polycrystalline HTSC+normal metal composites

Measurements of current–voltage characteristics (CVC) of Y 3/4Lu 1/4Ba 2Cu 3O 7+BaPbO 3 and Y 3/4Lu 1/4Ba 2Cu 3O 7+BaPb 0.9Sn 0.1O 3 composites modelling network of superconducting–normal metal–superconducting (S–N–S) junctions in effectively `clean' and `dirty' limits, respectively, have been performed. Essential difference of CVCs for these composites is observed in spite of the identical preparation technique and experimental conditions. It is shown that the theory for S–N–S junctions [R. Kummel, U. Gunsenheimer, R. Nicolsky, Phys. Rev. B, 42 (1990) 3932] well describes the experimental CVCs of the composites in both cases.