Anomalous Tunneling Characteristics

Abstract

Quasiparticle tunneling¹ into superconducting transition metals often shows current—voltage characteristics differing from the ideal curves: an excess current peak or “knee” occurring at biases near the sum of the half-energy gaps of the two superconducting electrodes. In the present work we give evidence that this knee is probably caused by excess adsorbed oxygen in the oxide insulating barrier. Its presence and temperature and magnetic field dependence can be explained by a simple physical model considering impurity energy states in the junction barrier. The knee is most easily identified as an extra dip in the derivative of the characteristic (Fig. 1.).

Supported by the Office of Naval Research and the National Science Foundation.