Superconducting diodes, characterized by the unidirectional supercurrent flow, are essential components for constructing energy-efficient superconducting circuits. Although the superconducting diode effect has been reported in a wide variety of platforms, its implementation usually requires an external magnetic field, cryogenic temperatures and elaborate device geometries, which significantly limit practical applications. Here, we report an intrinsic, field-free superconducting diode effect in a simple van der Waals FeSe nanosheet. Systematic investigations of sample geometries, residual magnetic fields, Joule heating effects, random vortex trappings, and electrodes or interfacial contacts reveal that the field-free superconducting diode effect originates from the time-reversal-symmetry breaking in the superconducting state of the FeSe nanosheet. The intrinsic field-free superconducting diode effect provides strong evidence of time-reversal-symmetry breaking in FeSe nanosheets. Furthermore, the field-free superconducting diode manifests a stable half-wave rectification performance after the 400-cycle operation and maintains the same polarity over a wide range of both positive and negative magnetic fields, which can tolerate ubiquitous stray fields in electrical circuits. The intrinsic field-free superconducting diode effect in a single van der Waals FeSe nanosheet with a simplified device architecture holds considerable promise for paving the way to practical, scalable superconducting diodes in ultra-low-power electronics.

With the explosive expansion of information, there is a growing need for non-volatile memories with high storage density and reconfigurability. Emerging two-dimensional (2D) ferroelectric materials enable the design of various high-performance functional devices that can potentially address these challenges. Here, we report a ferroelectric semiconductor floating-gate transistor based on an α-In₂Se₃/hexagonal boron nitride (h-BN)/multi-layered graphene (MLG) van der Waals heterostructure on a SiO₂/Si substrate. Thanks to the coexistence of both out-of-plane and in-plane polarizations in an α-In₂Se₃ channel, pairs of polarization-modulated channel resistance states can be successfully generated between the floating-gate-modulated on and off states, which can be programmed by either vertical gate pulses or planar drain pulses. These features enable a 2-bit multi-level memory in both three-terminal or two-terminal operational modes, significantly increasing the storage density and reconfigurability. The present results introduce a new design degree of freedom for floating-gate memories and provide fresh insights into future non-volatile memory technologies.

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.