Field-free superconducting diode effects in structurally asymmetric van der Waals Josephson junctions

The superconducting diode effect (SDE), characterized by the unidirectional and dissipationless flow of supercurrent, has recently garnered significant attention in the exploration of unconventional superconductors and hybrid quantum systems. While the prevailing understanding attributes the SDE to the simultaneous breaking of time-reversal and inversion symmetries, our investigation of the SDE in all-2D van der Waals (vdW) Josephson junctions (JJs) with 2D vdW superconductor NbSe₂ reveals a fundamentally different mechanism. In this study, we demonstrate that the observed non-reciprocal supercurrents are uniquely controlled by the twist angle between NbSe₂ layers, rather than being determined by tunnel barriers such as MoS₂. This pronounced twist-angle dependence of field-free SDEs points to an intrinsic symmetry-breaking mechanism in vertical NbSe₂–NbSe₂ JJs, closely tied to the anisotropic superconducting gap structure inherent to 2D vdW superconductors. Our findings redefine the origin of superconducting diode effects in vdW JJs, paving the way for the development of next-generation quantum technologies based on 2D vdW materials and their heterostructures.