Overdamped Van der Waals Josephson Junctions by Area Engineering

Josephson junctions (JJs) are the building blocks of superconducting quantum devices. The current technology exploits defective systems and interfaces—conventional superconducting and insulating thin films—resulting in compromised coherence times. JJs are realized by stacking a few‐layered NbSe 2 flakes, a highly crystalline layered system that exploits the van der Waals (vdW) gap between the flakes as the tunnel barrier, resulting in defect‐free JJs and high‐quality superconducting devices. For quantum technology, overdamped JJs are required, and their realization demands precise control of junction capacitance. Since the vdW gap between overlapping flakes is fixed, controlling the McCumber parameter characterizing the damping requires engineering the junction area using microfabrication techniques. In contrast, most of the vdW superconductors, including NbSe 2 , are highly unstable against conventional sample fabrication processes. In this article, both underdamped and overdamped NbSe 2 –NbSe 2 JJs are demonstrated by controlling the junction area. A minimally invasive microfabrication procedure, postjunction formation, to control the junction area precisely is devised. The Fraunhofer patterns in the junction voltage against a parallel magnetic field confirm the formation of high‐quality JJs. The results show that sample fabrication recipe has preserved the material qualities and paved the way for realizing scalable JJ devices on NbSe 2 and similar systems.