Josephson Coupling to 2D Magnets

Superconductor/ferromagnet/superconductor (S/F/S) junctions enable the study of superconducting proximity effect in a magnetic material, 0–π Josephson phase transition, and their applications in quantum computing. To study the proximity effect, clean interfaces are required. We construct a lithography-free, polymer-free van der Waals vertical heterostructure of NbSe₂/CrSBr/NbSe₂ to investigate the interplay between superconductivity and magnetism. NbSe₂ is an Ising superconductor with a high in-plane upper critical field above 8T. CrSBr is a ferromagnet in the monolayer limit and an A-type antiferromagnet in thicker layers with a coercive field below 1T (2-5 layers) along its b-axis. Therefore, a NbSe₂/CrSBr/NbSe₂ heterostructure becomes an S/F/S junction in a small in-plane magnetic field. We mechanically exfoliate NbSe₂ and CrSBr, characterize them with optical and atomic force microscopy, and then stack them using a dry-transfer pick-up technique, all inside an Argon-filled glovebox to protect against oxidation. Our next step is to fabricate them into devices and perform low-temperature transport measurements to study proximity-induced superconductivity in CrSBr. Our work builds on the understanding of the coexistence of superconductivity and magnetism in the 2D limit.