DIFFERENTIAL CONDUCTANCE OF NORMAL METAL-INSULATOR-D-WAVE SUPERCONDUCTOR JUNCTIONS WITH INTERFACE ROUGHNESS

Within the framework of Blonder-Tinkham-Klapwijk (BTK) model and takin g into account the interface roughness, we calculate the differential conductance of normal metal-insulator-d-wave superconductor junctions. We find that the tunneling spectrum depends strongly on both the inci dent angle of electrons and the crystalline axis orientation of the su perconductor, and exhibits the zero-bias anomaly under suitable arrang ements. Interestingly, even in the absence of the insulating layer, th e tunneling spectrum of normal metal-d-wave superconductor junctions d iffers significantly from that for normal metal-s-wave superconductor due to the interface roughness. Moreover, both the tunnel conductance peak at the energy gap and the zero-bias conductance peak are suppress ed by the interface roughness. Our results can explain many experiment al measurements on the tunneling spectra of high-T-c superconductors.