Intrinsic field-free superconducting diode effect in a simple van der Waals FeSe nanosheet

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.