Spatially Varying Energy Gap in the CuO Chains ofYBa2Cu3O7−xDetected by Scanning Tunneling Spectroscopy

Abstract

Current-imaging tunneling spectroscopy (CITS) was performed on cold-cleaved single crystals of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ at 20 K. CITS data include $I\left(V\right)$ curves taken simultaneously with a topographic scanning tunneling microscopic image. $I\left(V\right)$ curves taken on CuO chains show an energy gap of about 20 meV which disappears near oxygen vacancies. We explain several features of large-junction $I\left(V\right)$ measurements, photoemission spectroscopy, and single-point $I\left(V\right)$ spectroscopy in terms of local effects detected by our CITS measurements. Finally, we consider the possibilities that this energy gap is due to either a charge-density wave or proximity-coupled superconductivity from the ${\mathrm{CuO}}_2$ planes.