Planar graphene-NbSe$_2$ Josephson junctions in a parallel magnetic field

TL;DR

This study demonstrates that planar graphene-NbSe2 Josephson junctions can sustain supercurrent under extremely high in-plane magnetic fields, revealing new regimes of 2D superconductivity and potential for advanced quantum device applications.

Contribution

The paper introduces a novel all van der Waals 2D Josephson junction with graphene and NbSe2 that operates under high in-plane magnetic fields, enabling exploration of Zeeman effects in 2D superconductors.

Findings

Supercurrent persists up to 8.5 T in parallel magnetic field.

Critical current shows suppression and recovery with increasing field.

Theoretical analysis includes Zeeman-induced 0-$ extpi$ transitions and ripple effects.

Abstract

Thin transition metal dichalcogenides sustain superconductivity at large in-plane magnetic fields due to Ising spin-orbit protection, which locks their spins in an out-of-plane orientation. Here we use thin NbSe$_2$ as superconducting electrodes laterally coupled to graphene, making a planar, all van der Waals two-dimensional Josephson junction (2DJJ). We map out the behavior of these novel devices with respect to temperature, gate voltage, and both out-of-plane and in-plane magnetic fields. Notably, the 2DJJs sustain supercurrent up to $H_\parallel$ as high as 8.5 T, where the Zeeman energy $E_Z$ rivals the Thouless energy $E_{Th}$, a regime hitherto inaccessible in graphene. As the parallel magnetic field $H_\parallel$ increases, the 2DJJ's critical current is suppressed and in a few cases undergoes suppression and recovery. We explore the behavior in $H_\parallel$ by considering theoretically two effects: a 0-$\pi$ transition induced by tuning of the Zeeman energy and the unique effect of ripples in an atomically thin layer which create a small spatially varying perpendicular component of the field. The 2DJJs have potential utility as flexible probes for two-dimensional superconductivity in a variety of materials and introduce high $H_\parallel$ as a newly accessible experimental knob.