TUNNELING SPECTROSCOPY INTO SUBSTITUTED Y-BA-CU-O SYSTEMS

We have studied the tunneling characteristics of Gd and Al substituted YBa2Cu3O7-delta single crystals with T(c)=90 K and 80 K respectively. The high-T(c) superconductors were etched 30 min in a 1% Br solution in methanol and the tunnel barriers were formed by exposing the crysta ls to the ambient atmosphere for about 30 min. Pb film counterelectrod es were thermally evaporated through a metallic mask. No relevant diff erences have been found in the differential resistance vs voltage of u ndoped 90 K and Gd junctions, so confirming that Gd is substituting fo r Y. A different behavior has been found in the Al doped junctions tha t show smeared structures of reduced amplitude.