Point-contact electron tunneling into the high-Tc superconductor Y-Ba-Cu-O

We report results of a study of electron tunneling into bulk samples of the new high-T_c superconductor Y-Ba-Cu-O using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 2∆=100 meV), implying 2∆/k_CT_c~13. Similar values were found previously by us for La-Sr-Cu-O. We also see Structure in the I-V curves similar to that seen in La-Sr-Cu-O. On the basis of the asymmetries observed in the I-V characteristics, we believe that the natural tunneling barrier on this material is of the Schottky type.