Tunneling characteristics of YBa/sub 2/(Cu/sub 1-x/Fe/sub x/)/sub 3/O/sub y/ junctions

The authors have measured the tunneling characteristics of planar junctions realized on YBa/sub 2/(Cu/sub 1-x/Fe/sub x/)/sub 3/O/sub y/ single crystals with x=0.04. In comparison with the undoped 90 K phase of this material, the conductance curves of the doped junctions show gap-like structures broadened and reduced in amplitude. This behavior is similar to what has been observed in junctions fabricated on YBa/sub 2/Cu/sub 3/O/sub 7- delta / single crystals with T/sub c/=60 K. At low temperatures the background conductance is linear up to about 100 mV and shows a parabolic behavior for higher voltages, as found in the undoped 90 K system. From the analysis of the parabola, the barrier height and thickness are deduced. In the doped junctions anomalies are frequently observed as a conductance peak centered at zero-bias. They appear to result from scattering that involves spin exchange between tunneling electrons and Fe ions localized at the metal-oxide interface.<>