Vertical Nb Josephson junctions fabricated by direct metal deposition on both surfaces of freestanding graphene layers

TL;DR

This paper presents a novel fabrication method for vertical Nb/multilayer graphene/Nb Josephson junctions using a freestanding van der Waals membrane, enabling pristine interfaces and scalable device production without ambient exposure.

Contribution

It introduces a double-sided processing technique for creating vertical Josephson junctions with elemental superconductors on suspended graphene layers, avoiding interface contamination.

Findings

Devices show clear Josephson coupling with reproducible supercurrents.

Critical current exhibits temperature dependence consistent with short-junction behavior.

Magnetic interference patterns confirm well-defined junction geometry.

Abstract

Vertical integration of superconducting electronics requires fabrication strategies that preserve pristine interfaces while accommodating oxidation-sensitive elemental superconductors. However, existing van der Waals-based vertical Josephson junctions largely rely on transfer-based assembly schemes that are incompatible with elemental materials such as niobium (Nb). Here, we introduce a freestanding van der Waals membrane architecture that enables deposition-based fabrication of vertical Josephson junctions through double-sided processing of a single suspended two-dimensional layer. Using multilayer graphene suspended across lithographically defined through-holes in a SiNx membrane, we realize vertical Nb/multilayer graphene/Nb Josephson junctions without ambient exposure of buried interfaces. The resulting devices exhibit clear Josephson coupling, including reproducible supercurrents and a temperature dependence of the critical current consistent with short-junction behaviour. Well-defined magnetic interference patterns governed by the membrane-defined aperture geometry, together with sub-gap features that track a Bardeen-Cooper-Schrieffer (BCS)-like superconducting gap, further confirm the junction quality. This platform establishes a scalable route to vertical superconducting devices based on oxidation-sensitive elemental superconductors and van der Waals materials.