ASYMMETRY AND QUASI-LINEAR BACKGROUND OF DIFFERENTIAL CONDUCTANCE CHARACTERISTICS OF HIGH-T-C-SUPERCONDUCTOR METAL TUNNEL-JUNCTIONS/

The inelastic component of differential conductivity of a tunnel junct ion is studied theoretically in a wide voltage range. A quadratic depe ndence (similar to\V\V) of differential conductivity on bias voltage V was found in addition to the linear one. The sign of the quadratic te rm depends on both the sign of bias voltage and the ratio of Fermi ene rgy to the parameter of the tunneling barrier strength. This leads to asymmetry of differential characteristics even if the barrier is recta ngular. Good agreement was obtained between our theoretical results an d experimental data observed on high-T-c-superconductor/metal as well as on Ni-NiO-Pb tunnel junctions.