Researchers report a superconducting diode that does not rely on a weak-link junction. The device is built from atomically flat van der Waals (vdW) crystals and shows non-reciprocal supercurrent — meaning current flows with zero resistance more easily in one direction than the other. The diode’s polarity can be set by the magnetization of an adjacent ferromagnet, and the team used the effect to demonstrate a two-input exclusive-NOR (XNOR) logic operation.

To make the diode the authors stacked a thin flake of the superconductor NbSe between two layers of the ferromagnet Fe3GeTe2 (abbreviated F3GT), forming a F3GT/NbSe/F3GT trilayer. The NbSe flake was about 35 nm thick and the two F3GT layers were deliberately different in thickness (about 18 nm and 231 nm) to break structural symmetry across the superconductor. Electrical measurements on the bare NbSe layer showed asymmetric critical currents when the ferromagnet was pre-magnetized in opposite directions, and the polarity of that asymmetry flipped when the F3GT spin orientation was reversed.

At a technical level the diode effect requires breaking certain symmetries: inversion symmetry (left-right symmetry) and time-reversal symmetry (the symmetry that links forward and backward time). In this device those symmetries are broken by the magnetic proximity of F3GT and by the structural asymmetry of the stack. The authors point to a picture in which Cooper pairs (the bound electron pairs that carry superconducting current) can acquire a finite center-of-mass momentum under these conditions. That finite-momentum pairing can produce a different critical current for the two current directions and so a diode-like response. The paper reports a diode efficiency as large as 29.7% at an applied field of 50 mT, a coercive field of about 0.28 T in the non-reciprocal response, and a field-free rectification whose polarity is set by the remnant magnetization of F3GT.