c-axis Josephson tunneling between Bi2Sr2CaCu2O8+x and Pb

Abstract

We have fabricated Josephson tunnel junctions between Bi2Sr2CaCu2O8+x (BSCCO) single crystals and Pb. Current flow is perpendicular to the CuO2 double layers of the BSCCO single crystal. The surface of the crystals used is almost atomically flat with less than one half unit-cell growth step per 50 μm. At low temperatures, the current-voltage characteristics exhibit a well-developed Pb gap as well as a nonzero Josephson current. In external magnetic fields oriented parallel to the junction barrier the critical current follows closely a Fraunhofer diffraction pattern indicating that the critical current density is homogeneous over the whole junction area. In external microwave fields, Shapiro steps appear at voltages that are multiples of fΦ0 showing that the Josephson currents are caused by first-order tunneling processes. The results strongly indicate that the superconducting order parameter of BSCCO has a nonzero s component. The product of critical current Ic and normal-state resistance RN of the junctions ranged between 0.5 and 8 μV, with an average value of 2.8 μV. An analysis of the IcRN products and of Ic vs temperature suggests that the s component is about three orders of magnitude smaller than the full order parameter that is generally presumed to have dx2−y2 symmetry.

Source-reported materials — not catalogue approval

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