Josephson Effect in NbS${}_2$ van der Waals Junctions

Van der Waals (vdW) Josephson junctions can possibly accelerate the development of advanced superconducting device that utilizes the unique properties of two-dimensional (2D) transition metal dichalcogenide (TMD) superconductors such as spin-orbit coupling, spin-valley locking. Here, we fabricate vertically stacked NbS${}_2$/NbS${}_2$ Josephson junctions using a modified all-dry transfer technique and characterize the device performance via systematic low-temperature transport measurements. The experimental results show that the superconducting transition temperature of the NbS${}_2$/NbS${}_2$ Josephson junction is 5.84 K, and the critical current density reaches 3975 A/cm${}^2$ at 2K. Moreover, we extract a superconducting energy gap $\mathrm{\Delta }=0.58$ meV, which is considerably smaller than that expected from the single band s-wave Bardeen-Cooper-Schrieffer (BCS) model ($\mathrm{\Delta }=0.89$ meV).