Subgap Conductivity of a Superconducting-Normal Tunnel Interface

TL;DR

This paper investigates how the layout of electrodes near a superconducting-normal tunnel interface influences subgap electron tunneling, highlighting interference effects related to the coherence length.

Contribution

It introduces a new approach to evaluate subgap current considering electrode layout and interference effects, independent of tunnel barrier properties.

Findings

Subgap current depends on electrode layout due to interference.

Interference effects are governed by the coherence length.

The developed method allows for layout-specific subgap current evaluation.

Abstract

At low temperatures, the transport through a superconducting-normal tunnel interface is due to tunneling of electrons in pairs. The probability for this process is shown to depend on the layout of the electrodes near the tunnel junction, rather than on properties of the tunnel barrier. This dependence is due to interference of the electron waves on a space scale determined by the coherence length, either in the normal or the superconducting metal. The approach developed allows us to evaluate the subgap current for different layouts of interest.