Zero Bias Anomaly and Preferred Surface Grain Orientation of YBa₂Cu₃O_7-δ Ceramics

Abstract

The zero bias anomaly dependent on the preferred surface grain orientation of YBa2Cu3O7-δ ceramics has been investigated in the conductance curve of the tunneling characteristics. A tunnel junction was fabricated by evaporating Al metal onto the ceramics sample and then annealed to remove the oxygen-deficient layer. The preferred orientation and the oxygen deficiency on the surface were examined based on X-ray diffraction patterns and X-ray photoelectron spectra. There exist oriented grains with their c-plane parallel to the ceramics sample surface. These surface layers are oxygen-deficient. Using the junction fabricated on the oxygen-deficient grains, the zero bias anomaly appears on the dynamic conductance curve of the tunneling characteristics. This anomaly disappears when the junction is fabricated after mechanical polishing of the surface and annealed. One of the sources of zero bias anomaly is the existence of oxygen-deficient grains on the YBa2Cu3O7-δ surface.