Influence of Quantum Fluctuations on Phase Coherent Andreev Tunneling

TL;DR

This paper investigates how quantum fluctuations and mesoscopic interference affect subgap conductance in a normal metal-superconductor tunnel junction, revealing a non-monotonic bias dependence due to competing effects.

Contribution

It introduces a detailed analysis of the interplay between quantum environmental fluctuations and mesoscopic interference in subgap transport.

Findings

Quantum fluctuations suppress subgap conductance at low bias.

Mesoscopic interference enhances conductance with decreasing bias.

The conductance exhibits a non-monotonic bias dependence.

Abstract

We study the subgap transport properties of a small capacitance normal metal-superconductor tunnel junction coupled to an external electromagnetic environment. Mesoscopic interference between the electrons in the normal metal strongly enhances the subgap conductance with decreasing bias voltage. On the other hand, quantum fluctuations of the environment destroy electronic phase coherence and suppress the subgap conductance at low bias (Coulomb blockade).The competition between charging effects and mesoscopic interference leads to a non-monotonic dependence of the differential subgap conductance on the applied bias voltage. This feature is pronounced, even if the coupling to the environment is weak and the charging energy is small.