SPATIALLY VARYING ENERGY-GAP IN THE CUO CHAINS OF YBA2CU3O7-X DETECTED BY SCANNING TUNNELING SPECTROSCOPY

Current-imaging tunneling spectroscopy (CITS) was performed on cold-cl eaved single crystals of YBa2Cu3O7-x at 20 K. CITS data include I(V) c urves taken simultaneously with a topographic scanning tunneling micro scopic image. I(V) curves taken on CuO chains show an energy gap of ab out 20 me V which disappears near oxygen vacancies. We explain several features of large-junction I(V) measurements, photoemission spectrosc opy, and single-point I(V) spectroscopy in terms of local effects dete cted by our CITS measurements. Finally, we consider the possibilities that this energy gap is due to either a charge-density wave or proximi ty-coupled superconductivity from the CuO2 planes.