Decoupling Josephson Coupling and Supercurrent Nonreciprocity in Twisted NbSe2/NbSe2 van der Waals Junctions

The microscopic origin of supercurrent nonreciprocity in van der Waals Josephson junctions remains under debate, particularly regarding the role of twist-angle engineering. Here, we investigate twisted NbSe2/NbSe2 vertical Josephson junctions with controlled crystallographic alignment and clean interfaces. High-resolution transmission electron microscopy directly determines the twist angle and interface quality. While Josephson coupling exhibits a pronounced twist-angle dependence, the supercurrent diode efficiency remains small and shows no systematic angular dependence. In contrast, enhanced diode responses emerge in weakly coupled junctions with reduced transparency and interfacial disorder. Deliberate interface degradation further enhances the diode efficiency to nearly 30% and produces irregular magnetic-field dependence. These results demonstrate a clear decoupling between Josephson coupling and supercurrent nonreciprocity, indicating that interfacial disorder rather than twist-angle-controlled momentum matching plays a dominant role in the observed diode response. Our findings establish an important benchmark for understanding nonreciprocal superconducting transport in van der Waals Josephson devices in the future.