Topography and local conductance images of YBa₂Cu₃O₇ crystals fractured in ultra high vacuum

Atomic-scale topography and local dynamic conductance images of polycrystalline YBa2Cu3O7 samples fractured in ultra high vacuum are obtained with a cross-sectional scanning tunneling microscope. Topographic features are found which consist of strips with a 12 Å periodicity. Simultaneous measurements of normalized conductance (d In I/dV) on these surfaces exhibit a sharp contrast from strip to strip. The corresponding tunneling spectra at these areas show an alternation of metallic and semiconducting characteristics. Possible implication of the results on the basic understanding of high temperature superconductivity is discussed. © 1989.