Study of the Tunneling Characteristics of Ba1-xKxBiO3Superconducting Thin Films Based on the Gap-Energy Distribution Model

The broadening of the gap edge in the conductance-voltage ( dI/ dV-V) characteristics for native-barrier Ba1-xKxBiO3-gold (BKBO//Au) and MgO-barrier Ba1-xKxBiO3-gold (BKBO/MgO/Au) junctions was investigated by using a gap-energy distribution model where the inhomogeneity of the energy gap ? at the junction interface was taken into consideration. It was demonstrated that the broadening of the dI/ dV-Vcurves and their temperature dependence (T<2TC/3) in both junctions could be explained by assuming the Gaussian distribution of gap energies (at T=0 K) with ?0(0)=3.1 meV, ??=0.9 meV for the BKBO//Au junction and ?0(0)=3.5 meV, ??=1.1 meV for the BKBO/MgO/Au junction, where ?0(0) and ?? represent the center point and the width of the distribution, respectively. It was found that the value ?? could be regarded as a criterion for the quality of the tunneling junction.