Directional in-plane tunneling in oxygen-deficient YBa₂Cu₃O_6.6/YBa₂Cu_2.55Fe_0.45O_y/YBa₂Cu₃O_6.6 edge junctions

In-plane tunneling measurements of superconductor-insulator-superconductor (SIS)-type oxygen-deficient edge junctions made of YBa₂Cu₃O_6.6 as the superconductor and YBa₂Cu_2.55Fe_0.45O_y as the barrier are reported. Two types of junctions were prepared in which transport is either along the (100) or the (110) direction. The dynamic conductance dI/dV shows a gaplike structure in the (100) junctions, while a zero-bias peak is observed in the (110) junctions. At energies below ∼2.5Δ₀ the results were found to be consistent with the Blonder, Tinkham, and Klapwijk model, extended by Tanaka and Kashiwaya to the case of d_x²-y²-wave superconductivity. At higher energies the behavior of the dynamic conductance is explained as due to a self-heating effect inside the junction.