Field-Free Superconducting Diode Effect in 45°-Twisted FeSe van der Waals Josephson Junctions.

The iron-based superconductor FeSe has garnered considerable attention, in no small part due to its rich physics as well as the unique coexistence of superconductivity and nematicity. The recent discovery of the superconducting diode effect (SDE)-a non-reciprocal critical current with respect to the bias direction-requires simultaneous breaking of time-reversal symmetry (TRS) and inversion symmetry (IS), making it a powerful transport signature of broken symmetries in superconductors. Notably, most reported SDEs rely on the application of an external magnetic field to break TRS, which significantly limits their practical applications in integrated superconducting electronics. Here, we report a field-free SDE in 45°-twisted FeSe Josephson junctions below 3 K, evidenced directly by the even symmetric dependence of the asymmetric critical current on the magnetic field. Under temperature modulation, the SDE is progressively suppressed and ultimately exhibits a polarity reversal at 2.2 K. Our findings provide compelling transport evidence for the field-free SDE in iron-based superconductor FeSe, offering a promising platform for exploring symmetry-breaking physics and developing low-dissipation superconducting electronic devices.