Real-time observation of discrete Andreev tunneling events

TL;DR

This paper demonstrates real-time detection of Andreev tunneling events in a superconductor-normal metal junction, revealing higher-than-expected rates and partial interface contributions, supported by direct current measurements.

Contribution

It provides the first real-time observation of Andreev tunneling events and shows that transport occurs through only part of the interface, challenging uniform barrier assumptions.

Findings

Higher Andreev tunneling rates than expected for uniform barriers

Evidence that only part of the interface contributes to transport

Direct correlation with single-electron transistor measurements

Abstract

We provide a direct proof of two-electron Andreev transitions in a superconductor - normal metal tunnel junction by detecting them in a real-time electron counting experiment. Our results are consistent with ballistic Andreev transport with an order of magnitude higher rate than expected for a uniform barrier, suggesting that only part of the interface is effectively contributing to the transport. These findings are quantitatively supported by our direct current measurements in single-electron transistors with similar tunnel barriers.