Study of the tunneling characteristics of Ba1-xKxBiO3 superconducting 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 Delta at the junction interface was taken into consideration. It was demonstrated that the broadening of the dI/dV-V curves and their temperature dependence (T < 2T(C)/3) in both junctions could be explained by assuming the Gaussian distribution of gap energies (at T = 0 K) with Delta(0)(0) = 3.1 meV; delta Delta = 0.9 meV for the BKBO//Au junction and Delta(0)(0) = 3.5 meV, delta Delta = 1.1 meV for the BKBO/MgO/Au junction, where Delta(0)(0) and delta Delta represent the center point and the width of the distribution, respectively. It was found that the value delta Delta could be regarded as a criterion for the quality of the tunneling junction.