STM images of a superconducting Cu-O plane and the corresponding tunneling spectrum in Bi2Sr2CaCu2O8+δ

Abstract

Clear atomic images of Bi2Sr2CaCu2O8+δ cleaved surfaces have been observed at T=6 and 300 K by scanning tunneling microscopy (STM). The atomic images taken for bias voltages much lower than the Bi-O plane semiconducting gap Eg∼100 meV, corresponding to the Cu-O plane, indicate that the conduction electrons exist mainly in the Cu 3dx2−y2 and O 2pσ orbitals. Tunneling spectra have been also measured in the same processes as in the Cu-O plane STM image observations at T=6 K. The low-temperature spectra are in good agreement with that in a d-wave superconductor with an anisotropic Fermi surface on which the normal density of states N(kF) is largest (Nmax) for the maximum gap directions and decreases to ∼Nmax/2 for the node directions. This, combined with the result on the N(kF) anisotropy in photoemission experiments, is consistent with a dx2−y2 superconducting gap. © 1996 The American Physical Society.

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