c-axis Josephson tunneling between Bi2Sr2CaCu2O8+x and Pb

We have fabricated Josephson tunnel junctions between Bi(2)Sr(2)CaCu(2)O8(x) (BSCCO) single crystals and Pb. Current flow is perpendicular to the CuO 2 double layers of the BSCCO single crystal. The surface of the crystals us ed is almost atomically Bat with less than one half unit-cell growth step p er 50 mu m. At low temperatures, the current-voltage characteristics exhibi t a well-developed Pb gap as well as a nonzero Josephson current. In extern al magnetic fields oriented parallel to the junction barrier the critical c urrent follows closely a Fraunhofer diffraction pattern indicating that the critical current density is homogeneous over the whole junction area. In e xternal microwave fields, Shapiro steps appear at voltages that are multipl es of f Phi(0) showing that the Josephson currents are caused by first-orde r tunneling processes. The results strongly indicate that the superconducti ng order parameter of BSCCO has a nonzero a component. The product of criti cal current I-c and normal-state resistance R-N of the junctions ranged bet ween 0.5 and 8 mu V, with an average value of 2.8 mu V. An analysis of the IcRN products and of I-c vs temperature suggests that the s component is ab out three orders of magnitude smaller than the full order parameter that is generally presumed to have d(x2-y2) symmetry.