Zeeman effect induced 0-$\pi$ transitions in ballistic Dirac semimetal Josephson junctions

TL;DR

This paper demonstrates Zeeman effect induced 0-$$ transitions in ballistic Dirac semimetal Josephson junctions, showing magnetic field tuning of the junction's phase state and direct measurement of a non-sinusoidal current-phase relation.

Contribution

It reports the first observation of Zeeman effect driven 0-$$ transitions in Dirac semimetal-based Josephson junctions, highlighting magnetic control over phase states in ballistic systems.

Findings

Zeeman effect causes 0-$$ transitions in Bi$_{1-x}$Sb$_x$ junctions.

Sign changes in critical current modulation reveal phase shifts.

Non-sinusoidal current-phase relation observed, consistent with ballistic transport models.

Abstract

One of the consequences of Cooper pairs having a finite momentum in the interlayer of a Josephson junction, is $\pi$-junction behavior. The finite momentum can either be due to an exchange field in ferromagnetic Josephson junctions, or due to the Zeeman effect. Here, we report the observation of Zeeman effect induced 0-$\pi$ transitions in Bi$_{1-x}$Sb$_x$, 3D Dirac semimetal-based Josephson junctions. The large g-factor of the Zeeman effect from a magnetic field applied in the plane of the junction allows tuning of the Josephson junctions from 0- to $\pi$- regimes. This is revealed by sign changes in the modulation of the critical current by applied magnetic field of an asymmetric superconducting quantum interference device (SQUID). Additionally, we directly measure a non-sinusoidal current-phase relation in the asymmetric SQUID, consistent with models for ballistic Josephson transport.