Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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The paper presents a detailed discussion of the current-voltage characteristic of intrinsic Josephson junctions in Bi 2 Sr 2 CaCu 2 O 8ϩ␦ and Tl 2 Ba 2 Ca 2 Cu 3 O 10ϩ␦ . In these materials Josephson tunnel junctions are formed naturally between adjacent superconducting CuO 2 bilayers or trilayers. A typical sample consists of a stack of Josephson junctions. We explicitly show that all junctions inside a given sample have identical tunneling characteristics. We discuss the shape ͑general curvature͒ of the current-voltage characteristic in terms of a superconducting order parameter that has a predominant d x 2 Ϫy 2 symmetry. The I c R n product of the intrinsic Josephson junctions turns out to be 2-3 mV, about 10% of the maximum energy gap ⌬ 0 /e. The currentvoltage characteristic of every individual junction exhibits pronounced structures in the subgap regime. They are best explained by a recently proposed resonant coupling mechanism between infrared active optical c-axis phonons and oscillating Josephson currents.