Anomalies in Tunneling through Localized States

We study the I–V characteristics of normal-metal/insulator/superconductor (NIS) and superconductor/insulator/superconductor (SIS) junctions with InO_x as the insulator. The characteristics of both types of devices exhibit structure at sub-gap as well as above-gap biases. The voltage position of the above-gap structure seems to scale with the gap energy. SIS junctions exhibit only part of the above-gap structure. These effects are associated with the presence of localized states in the barrier region.