Direct STM mapping of the superconducting energy gap in single crystal BI2SR2CACU2O8+x

E. L. Wolf, A. Chang, Z. Y. Rong, Yu M. Ivanchenko, Farun Lu

Research output: Contribution to journalArticle

Abstract

Scanning tunneling spectroscopy applied to BiO cleavage planes of 90 K Tc BSCCO 2212 at 4.2 K simultaneously provides topography and local dI/dV spectra (superconducting DOS). The spectra, which are similar to recent photoemission spectra, confirm a large gap parameter Δ(x, y) associated with an apparently gapless DOS on the uppermost layer. Transverse spatial variations of Δ on a 100 Å scale are attributed to variations in BiO metallicity, presumably originating in oxygen stoichiometry variations in an unannealed crystal. We identify two characteristic dI/dV spectral shapes with regions of metallic and nonmetallic BiO layers, and can relate these by the McMillan model of the superconducting proximity effect. A sharply peaked spectral shape, similar to that observed in photoemission, is predicted for the metallic BiO layer induced superconducting by its proximity to the underlying CuO2 planes. The short mean free path and short coherence length imply that both tunneling and photoemission spectra are heavily weighted toward contributions from the BiO layer in fully metallic 2212. The present results and analysis thus suggest that the superconducting proximity effect influences the lineshapes seen by both techniques.

Original languageEnglish (US)
Pages (from-to)355-360
Number of pages6
JournalJournal of Superconductivity
Volume7
Issue number2
DOIs
StatePublished - Apr 1994

Keywords

  • Energy gap
  • high-temperature superconductor
  • scanning tunneling microscope
  • spatial variation

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Physics and Astronomy (miscellaneous)

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