Van der Waals Josephson Junction with sub-100nm channel length

The superconducting proximity coupling to unconventional materials enables the exploration of novel quantum phenomena relevant for quantum technologies. The realization of complex circuits requires highly transparent interfaces and the control of nanoscale dimensions. We etch narrow trenches in NbSe₂ and use van der Waals transfer to fabricate NbSe₂ -graphene-NbSe₂ lateral Josephson junctions with length L < 100 nm and width W. Cross-sectional transmission electron microscopy confirms minimal NbSe₂ oxidation. We observe gate-tunable critical current I_c with densities up to 700 nA µm⁻¹ in the heavy hole regime and the interference pattern of I_c in a perpendicular magnetic field. Because of the thin NbSe₂ flake and the small length of our junctions, the Fraunhofer flux period is given by 1.8Φ₀/W² instead of the conventional Φ₀/(L+2λ)W, where Φ₀ is the flux quantum and λ is London penetration length . This can be understood by using the Pearl length of 2D superconductors. Deviation from the conventional Fraunhofer pattern also includes lifted first nodes and sometimes missing higher nodes. Inhomogeneous supercurrent flow and flux trapping in the NbSe₂ may play a role. Our next step is to extend this non-invasive, polymer-free method to pattern superconducting circuits incorporating topological insulators and 2D magnets.