QUASI-PARTICLE TUNNELING PROPERTIES OF PLANAR YBA2CU3O7-DELTA PRBA2CU3O7-DELTA/HOBA2CU3O7-DELTA HETEROSTRUCTURES/

We report a demonstration of S-I-S quasiparticle tunneling in c-axis o riented planar junctions consisting of YBaCuO/PrBaCuO/HoBaCuO thin fil m heterostructures. In the conductance curves at low temperatures well developed peaks indicative of gap structures are found at +/-45 mV. T he high bias conductance shows flat dependence on energy and the best quality junction has a zero-bias conductance less than 0.05 of the nor mal state value. We discuss our spectra in the framework of a BCS-like density of states as well as in terms of a d(x)(2)-(2)(y) symmetry of the superconducting order parameter.