Gang Qiu1,2,Hung-Yu Yang1,Lunhui Hu3,Huairuo Zhang4,Chi-Yen Chen5,Yanfeng Lyu6,Peng Deng1,Sergiy Krylyuk4,Albert Davydov4,Ruixing Zhang3,Kang Wang1
University of California, Los Angeles1,University of Minnesota2,The University of Tennessee, Knoxville3,National Institute of Standards and Technology4,National Sun Yat-sen University5,Nanjing University of Posts and Telecommunications6
Gang Qiu1,2,Hung-Yu Yang1,Lunhui Hu3,Huairuo Zhang4,Chi-Yen Chen5,Yanfeng Lyu6,Peng Deng1,Sergiy Krylyuk4,Albert Davydov4,Ruixing Zhang3,Kang Wang1
University of California, Los Angeles1,University of Minnesota2,The University of Tennessee, Knoxville3,National Institute of Standards and Technology4,National Sun Yat-sen University5,Nanjing University of Posts and Telecommunications6
Iron-based high-Tc FeTe<sub>x</sub>Se<sub>1-x</sub> (FTS) has been proposed to host unconventional superconductivity. Recent scanning probe and ARPES experiments imply spontaneous time-reversal symmetry breaking in FTS systems. In this work, we report the field-free superconducting diode effect in FTS van der Waals Josephson junctions (vJJ). Non-reciprocal superconducting critical current can be observed in the absence of external magnetic field, which directly manifests spontaneous time-reversal symmetry breaking in FTS systems. The polarity and efficiency of the diode effect are also stochastic, which can be randomly reset by performing a thermal cycle above the superconducting critical temperature Tc. This suggests the time-reversal symmetry breaking ordering is closely tied to the superconducting states. The stochasticity also provides insights into ferromagnetic domain behaviors of superconducting surface states.