The emergence of superconducting diode effect (SDE) provides a new platform to investigate the intertwining among band topology, superconductivity, and magnetism, thereby establishing the foundation for achieving ultra-low dissipation devices and circuits. The realization of the tunable zero-field SDE in two-dimension (2D) devices is significant for 2D circuits, however, there has been great challenges in the appropriate materials synergy and fine device design. Here, we report a zero-field SDE in the van der Waals (vdW) heterostructure constructed by the Ising superconducting NbSe₂ and ferromagnetic Fe₃GeTe₂ with a large perpendicular magnetic anisotropy. Based on the valley-Zeeman spin-orbit interaction (SOI) in NbSe₂, the magnitude and polarity of the zero-field SDE can be modulated by altering the ferromagnetic properties of Fe₃GeTe₂ through the application of pre-magnetized out-of-plane magnetic fields. Furthermore, the stable half-wave rectification of square-wave currents is achieved by utilizing the tunable zero-field SDE in the Josephson junction-free structure. The tunable zero-field SDE in 2D heterostructures brings new opportunities for understanding the coexistence of superconductivity and time-reversal symmetry breaking, and for fabricating 2D ultra-low dissipation circuits.

Two-dimensional (2D) ferroelectric (FE) materials with relatively low switching barrier and large polarization are promising candidates for next-generation miniaturized nonvolatile memory devices. Herein, we screen out 39 new 2D ferroelectric materials, MX (M: Group III-V elements; X: Group V-VII elements), in three phosphorus-analogue phases including black phosphorene-like α-phase, blue phosphorus-like β-phase, and GeSe-like γ-phase using high-throughput calculations. Seven materials (α-SbP, γ-AsP, etc.) exhibit FE switching barriers lower than 0.3 eV/f.u., ferroelectric polarization larger than 2 × 10⁻¹⁰ C/m, and high thermodynamic stability with energy above hull smaller than 0.2 eV/atom. We find that the larger the electronegativity difference between M and X, the larger the ferroelectric polarization. Moreover, larger electronegativity differences result in lower in-plane piezoelectric stress tensor (e₁₁) for MX consisting of Group IV and VI elements and larger e₁₁ for those consisting of Group V elements. Further calculations predict a giant tunneling electroresistance in ferroelectric tunnel junction α-Sb(Sn)P/α-SbP/α-Sb(Te)P (1.26 × 10⁴%) and large piezoelectric strain coefficient in α-SnTe (396 pm/V), providing great opportunities to the design of non-volatile resistive memories, and high-performance piezoelectric devices.

Discovery of novel two-dimensional (2D) ferroelectric materials and understanding the mechanism are of vital importance for the design of nanoscale ferroelectric devices. Herein, we report the distinct geometric evolution mechanism of the newly reported M₂Ge₂Y₆ monolayers and find out a large group of 2D ferroelectric candidates based on this mechanism. The origination of the ferroelectricity of M₂Ge₂Y₆ is the vertical displacement of Ge-dimer in the same direction driven by a soft phonon mode of the centrosymmetric configuration. Interestingly, we find another centrosymmetric configuration which is dynamically stable but higher in energy comparing with the ferroelectric phase. The metastable centrosymmetric phase of M₂Ge₂Y₆ monolayers allows a new two-step ferroelectric switching path and may induce novel domain behaviors. Moreover, the ferroelectric M₂Ge₂Y₆ monolayers exhibit independently switchable dipoles and maintain their ferroelectricity after contacting with graphene electrodes, indicating their high application potentials in high-density storage. Furthermore, 16 ferroelectric (FE) M₂Ge₂Y₆ and 65 potential FE M₂Sn₂Y₆ monolayers are identified through high-throughput calculations. Our findings provide a new strategy for future discovery of novel 2D ferroelectric materials and also platforms for experimental design of related functional devices.