Suppressed Superconductivity of the Surface Conduction Layer in Bi2Sr2CaCu2O8+x Single Crystals Probed by c-Axis Tunneling Measurements
Abstract
We fabricated small-size stacks on the surface of Bi2Sr2CaCu2O8+x (BSCCO-2212) single crystals with the bulk transition temperature Tc90 K, each containing a few intrinsic Josephson junctions. Below a critical temperature Tc' ( Tc), 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 IV data of the weakened Josephson junction (WJJ) fits well to the tunneling characteristics of a d-wave superconductor(')/insulator/d-wave superconductor (D'ID) junction. Also, the tunneling resistance in the range Tc'<T<Tc agrees well with the tunneling in a normal metal/insulator/d-wave superconductor (NID) junction. In spite of the suppressed superconductivity at the surface layer the symmetry of the order parameter appears to remain unaffected.
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