Visualization of Macroscopic Ising Superconducting State in Superconductor-Graphene Junctions

Graphene-based two-dimensional van der Waals Josephson junctions with superconductors are hopeful for realizing versatile quantum devices. However, research on the junctions with Ising superconductors in atomic-layer transition metal dichalcogenides, whose superconductivity is resilient to strong in-plane magnetic fields, has remained elusive. Here the scanning tunneling microscopy study of Ising superconductivity in single-layer (SL) NbSe₂ island and its long-range proximity effect to the adjacent graphene with high spatial and energy resolution is reported. It is found that SL NbSe₂ island manifests as an Ising superconductor while the island area is larger than about 800 nm². Moreover, the superconducting proximity effect from the NbSe₂ island generates a superconducting gap in graphene, which can extend to over several tens of nanometers without obvious decay. Such a long-range proximity effect makes the intrinsically non-superconducting graphene as a superconductor. More intriguingly, such a superconducting gap can survive under strong in-plane magnetic fields, following the Ising behavior of that in SL NbSe₂. This work reveals a brand-new macroscopic Ising superconducting regime, opening perspectives for superconductor-based quantum devices with outstanding functionality.