SUBHARMONIC SHAPIRO STEPS AND NOISE IN HIGH-T-C SUPERCONDUCTOR JOSEPHSON-JUNCTIONS

An experimental investigation is made of the subharmonic Shapiro steps observed on the I-V curves of high-T-c superconductor Josephson junct ions and on the bias-voltage dependences of the rf noise and detector response when the junctions are subjected to external submillimeter ra diation. Structures of this type are ordinarily described by a nonsinu soidal current-phase relation, which is why subharmonic steps appear. Numerical modeling of the processes occurring in a Josephson junction by means of a simple current-phase relation, as in the case of an SNS junction, gives good agreement with experiment. The width of the chara cteristic Josephson generation line of the junction was estimated on t he basis of the noise dependences and the selective detector response. The width can be explained by taking into account the shot noise of t he tunneling component of the conductivity. A model of the conductivit y of a high-T-c superconductor Josephson junction, consisting of a tun nel junction with microshorts possessing metallic conductivity, is dis cussed. (C) 1998 American Institute of Physics. [S0021-3640(98)01417-0 ].