Correlation between d -wave pairing behavior and magnetic-field-dependent zero-bias conductance peak

We consistently observe a magnetic-field-dependent conductance peak at zero-bias voltage in a wide range of superconductor/noble-metal junctions fabricated from oxide superconductors (${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ and ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CaCu}}_{2}\mathrm{O}$) that have been reported to exhibit $d$-wave pairing behavior; however, no measurable peak appears in similar junctions made from an $s$-wave oxide superconductor $({\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4}).$ Explanations of this correlation are considered in terms of the Appelbaum-Anderson model for magnetic interface scattering and the midgap-state model for $d$-wave interface states.