ELECTRON-TUNNELING INTO 1-2-3 HTSC THIN-FILMS

We report on detailed tunneling measurements on thin film planar tunnel junctions of the type RE1Ba2Cu3O7/native oxide/Pb (RE = Y, Eu or Gd). The films were sputter deposited and chemically etched prior to the growth of the native oxide. The structural content of gaplike structure in the I-V characteristic was investigated by taking dI/dV and d3I/dV3 traces. By analysis of the temperature dependence and temperature smearing strong arguments could be provided that all the structures between +/- 50 mV measured at low temperature are due to density of states effects. On junctions prepared on 1-2-3 films with T(c) depressed either by partial oxygen depletion or by alloying we found that the gaplike structure was weakened but did not shift on the energy scale.