ELECTRON-TUNNELING AND TRANSPORT IN THE HIGH-TC SUPERCONDUCTOR Y1-XPRXBA2CU3O7-DELTA

We have performed tunneling measurements on single crystals of the superconducting cuprate Y1-xPrxBa2Cu3O7-delta. With increasing concentration of Pr, the structure seen in YBa2Cu3O7-delta in the energy region where a gap is expected, becomes even less pronounced (more ''gapless'') as the T(c) is reduced. In the vicinity of the supeconductor-insulator transition, in tunnel junctions of demonstrably high quality, this structure becomes very weak. We draw upon a strong analogy between this system and ion beam damaged YBa2Cu3O7-delta to discuss the results.