Study of YBCO/Au Surface Using Low-Temperature Scanning Tunneling Microscopy/Scanning Tunneling Spectroscopy

A low-temperature scanning tunneling microscope (LTSTM) has been used to study the surface electronic state of a 30-nm-thick Au film deposited on (103)-oriented YBCO thin film. Conductance spectra with the BCS-like dip induced by the superconductivity proximity effect were observed in a small area. Also, spectra with zero-bias conductance peaks were observed in another limited area. Most parts of the areas studied showed constant conductance spectra. Since this fact suggests the existence of a degraded layer on most surfaces of the YBCO film, the Josephson coupling in YBCO/Au/Nb is assumed to occur primarily in this degraded layer.