LOW-TEMPERATURE SCANNING TUNNELING TOPOGRAPHY OF YBA2CU3OX SUPERCONDUCTING FILMS

We have performed both topographic and spectroscopic measurements at 4.2 K on thin films of YBa2Cu3Ox with a scanning tunneling microscope. The films all had zero resistance temperatures in excess of 75 K. We found that, even at low temperatures, most of the surface of the films were conducting. Images were obtained at tunneling voltages as low as 2 mV with little effect on the resultant topography. Noisy patches, which are observed in some images, and result from unstable feedback response, indicate regions of reduced surface conductivity. Current-voltage curves obtained at different points indicate that superconductivity can extend out to the surface of the films. Despite excessive broadening resulting from charging effects, gap values as high as 20 meV were observed. © 1990, American Vacuum Society. All rights reserved.