Suppressed superconductivity of the surface conduction layer in Bi2Sr2CaCu2Os8+x single crystals probed by c-axis tunneling measurements

We fabricated small-size stacks on the surface of Bi(2)Sr(2)CaCu(2)ZO(8+x) single crystals with the bulk transition temperature T-c similar or equal to 90 K, each containing a few intrinsic Josephson junctions. Below a critical temperature T-c' (much less than T-c), we have observed a weakened Josephson coupling between the CuO2 superconducting double layer at the crystal surface and the adjacent one located deeper inside a stack. The quasiparticle branch in the I-V data of the weakened Josephson junction fits well to the tunneling characteristics of a d-wave superconductor (')-insulator-d-wave superconductor junction. Also, the tunneling resistance in the range T-c' < T < T-c agrees well with the tunneling in a normal-metal-insulator-d-wave superconductor junction. Ln spite of the suppressed superconductivity at the surface layer the symmetry of the order parameter appears to remain unaffected.