Strong Proximity Josephson Coupling in Vertically Stacked NbSe₂-Graphene-NbSe₂ van der Waals Junctions

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Two-dimensional (2D) layered materials enable novel device architectures through van der Waals (vdW) heterostructures.
• Inducing proximity superconductivity in non-superconducting materials is crucial for advanced electronic applications.
• Niobium diselenide (NbSe2) is a layered superconductor with potential for vdW heterostructures.

Purpose of the Study:

• To fabricate and characterize a vdW heterostructure for strong proximity-coupled Josephson junctions.
• To investigate the Josephson coupling properties at the interface of NbSe2 and graphene.
• To demonstrate the potential of dry-transfer stacking for creating high-quality superconducting interfaces.

Main Methods:

• Fabrication of vertically stacked NbSe2-graphene-NbSe2 heterostructures using vdW interlayer coupling.
• Characterization of interfacial properties, focusing on defect-free contacts and high transparency.
• Measurement of temperature dependence of critical current (Ic) and differential conductance.
• Analysis of subgap structures and magnetic field modulation of Ic.

Main Results:

• Achieved defect-free contacts with high interfacial transparency in the NbSe2-graphene-NbSe2 heterostructure.
• Demonstrated highly coherent proximity Josephson coupling mediated by the atomically thin graphene layer.
• Observed short and ballistic Josephson coupling characteristics, consistent with theoretical predictions.
• Confirmed strong Josephson coupling via a large critical current density (1.6 × 10^4 A/cm^2) and multiple Andreev reflections.

Conclusions:

• This work presents the first demonstration of strongly proximity-coupled Josephson junctions in a dry-transfer-stacked vdW heterostructure.
• The engineered NbSe2-graphene-NbSe2 interfaces exhibit exceptionally clean characteristics, enabling robust superconducting coupling.
• The findings pave the way for novel superconducting devices utilizing 2D materials and proximity effects.