STUDY OF POINT CONTACTS WITH AU-TIP ON YBA2CU3OX AND BI2SR2CACU2OY THIN-FILMS

Differential resistance - voltage characteristics (dV/dI-V) of thin fi lms YBa2Cu3Ox(YBCO) and Bi2Sr2CaCu2Oy(BSCCO) point contact junctions u sing an Au - tip were studied in order to investigate the surface prop erties of these high-Tc superconductors (HTS). The shape of these char acteristics confirms different nature of the point contact junctions. The YBCO/Au contacts have well defined insulating tunneling barriers, but BSCCO/Au contacts behave as metallic junctions. The experimental d V/dI-V characteristics can be fitted by Blonder-Tinkham-Klapwijk theor y describing transition and reflection of quasiparticles at an N-S int erface. However, better fitting is received if a broadening parameter GAMMA, characterizing the presence of scattering centers in HTS, is in cluded into the theory. Comparing the experimental and theoretical dat a we conclude, that BSCCO surface layers are chemically more stable th an those of YBCO. These results we interprete by stronger affinity of oxygen atoms in BSCCO than in YBCO material