Multiple Andreev reflections and Shapiro steps in a Ge-Si nanowire Josephson junction

TL;DR

This study demonstrates a Ge-Si nanowire Josephson junction exhibiting clear supercurrent, multiple Andreev reflections, and Shapiro steps, highlighting its potential for quantum computing and Majorana physics.

Contribution

The paper reports the fabrication and characterization of a Ge-Si nanowire Josephson junction with transparent contacts, showing multiple Andreev reflections and Shapiro steps, advancing understanding of superconductor-semiconductor interfaces.

Findings

Finite supercurrent observed in the junction.

Up to 23 Shapiro steps detected.

Multiple Andreev reflections up to sixth order.

Abstract

We present a Josephson junction based on a Ge-Si core-shell nanowire with transparent superconducting Al contacts, a building block which could be of considerable interest for investigating Majorana bound states, superconducting qubits and Andreev (spin) qubits. We demonstrate the dc Josephson effect in the form of a finite supercurrent through the junction, and establish the ac Josephson effect by showing up to 23 Shapiro steps. We observe multiple Andreev reflections up to the sixth order, indicating that charges can scatter elastically many times inside our junction, and that our interfaces between superconductor and semiconductor are transparent and have low disorder.