Van der Waals Ferromagnetic Josephson Junctions

TL;DR

This paper demonstrates the creation of van der Waals ferromagnetic Josephson junctions using layered NbSe2 and Cr2Ge2Te6, revealing magnetic control of superconducting properties and coexistence of different phase couplings.

Contribution

It introduces a novel vdW heterostructure-based ferromagnetic Josephson junction with tunable magnetic and superconducting interactions, enabling new studies of weak magnetism.

Findings

Hysteretic and oscillatory critical current behavior under magnetic fields.

Observation of coexistence of 0 and π phase coupling.

Control of magnetic properties via junction hysteresis.

Abstract

Superconductor-ferromagnet (S-F) interfaces in two-dimensional (2D) heterostructures present a unique opportunity to study the interplay between superconductivity and ferromagnetism. The realization of such nanoscale heterostructures in van der Waals (vdW) crystals remains largely unexplored due to the challenge of making an atomically-sharp interface from their layered structures. Here, we build a vdW ferromagnetic Josephson junction (JJ) by inserting a few-layer ferromagnetic insulator Cr2Ge2Te6 into two layers of superconductor NbSe2. Owing to the remanent magnetic moment of the barrier, the critical current and the corresponding junction resistance exhibit a hysteretic and oscillatory behavior against in-plane magnetic fields, manifesting itself as a strong Josephson coupling state. Through the control of this hysteresis, we can effectively trace the magnetic properties of atomic Cr2Ge2Te6 in response to the external magnetic field. Also, we observe a central minimum of critical current in some thick JJ devices, evidencing the coexistence of 0 and {\pi} phase coupling in the junction region. Our study paves the way to exploring the sensitive probes of weak magnetism and multifunctional building blocks for phase-related superconducting circuits with the use of vdW heterostructures.