Tunneling between Pb and c-axis oriented Bi 2Sr 2CaCu 2O 8 single crystals

We investigated c-axis tunnel junctions between Bi ₂Sr ₂CaCu ₂O _{8+ x} (BSCCO) single crystals and Pb. At low temperatures, the current-voltage characteristics exhibit a well developed Pb gap as well as a nonzero Josephson current. In magnetic fields the critical current follows closely a Fraunhofer diffraction pattern showing that the critical current density is homogeneous. In microwave fields, Shapiro steps appear at voltages that are multiples of hf/2e confirming that the Josephson currents are of first order. These results strongly indicate that the superconducting order parameter of BSCCO has a nonzero s-component.