Tunneling study through analysis of spatial variations of the pair potential in diffusive normal metal/insulator/high-Tc superconductor junctions

We report how spatial variations of the pair potential with an anisotropic symmetry influence tunneling conductance spectra in diffusive normal metal/insulator/dx2-y2-wave superconductor (DN/I/DS) junctions. A zero-bias conductance peak (ZBCP) was observed for the (1 1 0)-oriented interface in Ag/SiO/Bi2Sr2CaCu2O8+δ (Bi-2212) planar junctions. The experimental ZBCP was analyzed by the circuit theory, which was improved by the introduction of spatial variations of the pair potential near the junction interface between a DN conductor and a DS electrode. Our experimental results are well explained by the extended circuit theory for DN/I/DS junctions.