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Suppressed Superconductivity of the Surface Conduction Layer in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ Single Crystals Probed by {\it c}-Axis Tunneling Measurements

Nam Kim·Yong Joo Doh·Hyun-Sik Chang·Hu-Jong Lee
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Abstract

We fabricated small-size stacks on the surface of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (BSCCO-2212) single crystals with the bulk transition temperature $T_c$$\simeq$90 K, each containing a few intrinsic Josephson junctions. Below a critical temperature $T_c'$ ($\ll$ $T_c$), we have observed a weakened Josephson coupling between the CuO$_2$ superconducting double layer at the crystal surface and the adjacent one located deeper inside a stack. The quasiparticle branch in the $IV$ data of the weakened Josephson junction (WJJ) fits well to the tunneling characteristics of a d-wave superconductor($'$)/insulator/d-wave superconductor (D$'$ID) junction. Also, the tunneling resistance in the range $T_c'$$<$$T$$<$$T_c$ 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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Nam Kim, Yong Joo Doh, Hyun-Sik Chang, Hu-Jong Lee. 1998-08-11. Suppressed Superconductivity of the Surface Conduction Layer in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ Single Crystals Probed by {\it c}-Axis Tunneling Measurements. https://doi.org/10.1103/physrevb.59.14639

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