Performance of ultra-flat superconducting layered transition metal dichalcogenide tunneling devices.

We present data on superconducting tunneling van der Waals heterostructures fabricated by stacking the superconducting transition-metal dichalcogenide (TMD), NbSe$_2$ with insulating BN. Such devices are of interest due to the atomically-flat and clean interfaces achievable in van der Waals heterostructures. In comparison, the interface uniformity of high quality Al/AlOx/Al junctions, which are often used to make superconducting qubits, depend on Al and AlOx grains with sizes between 10-100nm leading to uncertainty in the junction's characteristics. Additionally, the performance of Al/AlOx/Al junctions can degrade over short time scales with exposure to an oxygen environment or as oxygen diffuses outwards from the tunnel barrier. We reveal ways in which encapsulated S-I-S junctions in van der Waals heterostructures can be expected to improve upon these difficulties.