Conductance Peak at Zero-Bias in Ag -SiO -Bi₂Sr₂CaCu₂O_8-x Planar Tunnel Junctions

Abstract

Two kinds of junctions were fabricated on a single crystal and a polycrystal of Bi₂Sr₂CaCu₂O_8-x. The tunneling conductance characteristics, G(V) were measured for the former junction at temperatures from 4.2 K to 100 K, and for the latter one at temperatures from 8.7 K to 90 K. It was found that the conductance peak (CP) at zero-bias is observed for tunneling direction perpendicular to a c-axis, but is not observed for tunneling direction parallel to a c-axis. Kashiwaya et al. theoretically predicted that the junction fabricated on a d-wave superconductor can give various G(V) characteristics scattering from a s-wave like spectrum to a d-wave like one, and has CP under certain boundary condition. In the present investigation, the measured G(V) characteristics in the high T_c Bi-system superconductor were found to qualitatively agree with the theoretical prediction by Kashiwaya et al.