Field-free Josephson diode effect in NbSe2 van der Waals junction

Nonreciprocal transport is one of the cornerstones of modern electronics industry with semiconductor diode serving as the most celebrated representative. Recently, superconducting diode has been put forward to achieve nonreciprocal transport in the non-dissipative regime. However, most of superconducting diodes require the application of magnetic field, limiting their practical application. Here we report a field-free diode effect in the van der Waals Josephson junctions composed of 2H-NbSe2 thin flakes without extra barrier layers. The unexpected large asymmetric current-voltage profile at zero field is observed in both overdamped and underdamped Josephson junctions. Under magnetic fields, the asymmetry of critical current is suppressed with a sign reversal. The realization of field-free Josephson diode with high rectification ratio in such a simple configuration not only implies an implicit spontaneous time-reversal symmetry breaking effect that challenges the existing theories, but also provides a promising avenue for the development of superconducting electronics and quantum devices. Nonreciprocal transport is a fundamental property of semiconducting-based electronics and the possibility of extending this to superconducting circuits without external magnetic field is a promising but challenging field of research. Here, the authors report a field-free superconducting diode effect for 2H-NbSe2 Josephson junctions with the results suggesting the existence of spontaneous time-reversal symmetry breaking.