Gate controlled anomalous phase shift in Al/InAs Josephson junctions

William Mayer,Joseph Yuan,Enrico Rossi,Javad Shabani,Kaushini S Wickramasinghe,Matthieu C Dartiailh

doi:10.1038/s41467-019-14094-1

William Mayer, Joseph Yuan + Show 4 more

Open Access

https://doi.org/10.1038/s41467-019-14094-1

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Abstract

In a standard Josephson junction the current is zero when the phase difference between superconducting leads is zero. This condition is protected by parity and time-reversal symmetries. However, the combined presence of spin–orbit coupling and magnetic field breaks these symmetries and can lead to a finite supercurrent even when the phase difference is zero. This is the so called anomalous Josephson effect—the hallmark effect of superconducting spintronics—which can be characterized by the corresponding anomalous phase shift. Here we report the observation of a tunable anomalous Josephson effect in InAs/Al Josephson junctions measured via a superconducting quantum interference device. By gate controlling the density of InAs, we are able to tune the spin–orbit coupling in the Josephson junction. This gives us the ability to tune the anomalous phase, and opens new opportunities for superconducting spintronics, and new possibilities for realizing and characterizing topological superconductivity.

Highlights

In a standard Josephson junction the current is zero when the phase difference between superconducting leads is zero
We have shown the capability to tune the anomalous phase shift of Josephson junction (JJ) formed by InAs and Al
This tunability results from the ability to vary the strength of the spin–orbit coupling via an external gate

Summary

Introduction

In a standard Josephson junction the current is zero when the phase difference between superconducting leads is zero. The combined presence of spin–orbit coupling and magnetic field breaks these symmetries and can lead to a finite supercurrent even when the phase difference is zero This is the so called anomalous Josephson effect—the hallmark effect of superconducting spintronics—which can be characterized by the corresponding anomalous phase shift. A hybrid system, combining spin–orbit coupling and superconductivity, results in a much richer physics where phase, charge current, and spin are all interdependent This gives rise to new phenomena such as an anomalous phase shift which is the hallmark effect of superconducting spintronics[1]. The presence of spin–orbit coupling along with the application of an in-plane magnetic field can break these symmetries[7] This allows an anomalous phase (φ0), which means that with no current flowing there can be a non-zero phase across the junction or, at zero phase a current can flow[8,9]. In Bi2Se3, a topological insulator, large planar φ0-junction are possible, Bi2Se3 is not gate tunable

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