Bias voltage asymmetry of inelastic differential conductivity of HTS/metal tunnel junctions

The inelastic component of differential conductivity of a tunnel junction is theoretically studied in a wide voltage range. A quadratic dependence (similar to \V\V) of differential conductivity on bias voltage V is found additionally to the linear one. The sign of the quadratic term depends on both the sign of the bias voltage and the ratio of the Fermi energy to the parameter of the tunneling barrier strength. This leads to an asymmetry of differential characteristics even if the barrier is rectangular. Good agreement between our theoretical results and experimental data observed on HTS/metal tunnel junctions is obtained.