Abstract
Tunneling into high-temperature superconductors is shown to be a powerful spectroscopic probe of the unconventional supercoducting states. The planar tunneling is performed on the (100), (110), and (001) oriented YBCO/Insulator/Normal metal planar junctions and on the point contact junctions of the (001)-oriented BSCCO single crystals. The quasi-particle spectra are shown in the c-axis oriented junctions. The zero-bias conductance peak (ZBCP) is observed in the conductance spectra of the ab-plane junctions with fairly reproducibility. The temperature and magnetic field dependence of the ZBCP are also measured. However, the field-induced splitting of the ZBCP expected by the theory is not observed in our experiments.