TUNNELING SPECTROSCOPY WITH INTRINSIC JOSEPHSON-JUNCTIONS IN BI2SR2CACU2O8+DELTA AND TL2BA2CA2CU3O10+DELTA

The paper presents a detailed discussion of the current-voltage charac teristic of intrinsic Josephson junctions in Bi2Sr2CaCu2O8+delta and T l2Ba2Ca2Cu3O10+delta. In these materials Josephson tunnel junctions ar e formed naturally between adjacent superconducting CuO2 bilayers or t rilayers. A typical sample consists of a stack of Josephson junctions. We explicitly show that all junctions inside a given sample have iden tical tunneling characteristics. We discuss the shape (general curvatu re) of the current-voltage characteristic in terms of a superconductin g order parameter that has a predominant d(x2-y2) symmetry. The IcRn p roduct of the intrinsic Josephson junctions turns out to be 2-3 mV, ab out 10% of the maximum energy gap Delta(0)/e. The current-voltage char acteristic 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 pho nons and oscillating Josephson currents.