Fig. 1: Supercurrent diode effect in a van der Waals superconductor.

a Scheme of the typical device. The central constriction is 250 nm wide and 250 nm long. The x-direction is chosen to be that of the supercurrent, i.e., the constriction axis. The z-direction is perpendicular to the crystal plane. The device is fabricated starting from a stack of hBN (≈10 nm, tens of layers), NbSe₂ (2, 3 or 5 layers) and again hBN (tens of layers). b Optical micrograph of sample B. The dashed white contour highlights the NbSe₂ crystal. Electrodes are fabricated by edge contact techniques^27,31,47, while the constrictions are made by reactive ion etching. The yellow arrow indicates the supercurrent pathway. The scale bar corresponds to 5 μm. c Current–voltage characteristics (IVs) for opposite bias polarities (i.e., opposite current directions) measured on sample G in a 3-terminal configuration for zero out-of-plane field B_z. The sweep direction is always from zero to finite bias. A contact resistance R_c = 1 kΩ has been subtracted. d Similar measurements, but for B_z = 32.5 mT. Notice the difference between the two critical currents. e Same as in panel (d), but with opposite field orientation. Notice that the role of the two bias polarities now is swapped. f Absolute critical current for positive (black) and negative (red) bias as a function of B_z. Each value is the average of 10 consecutive measurements. The critical current is maximal for a nonzero B_z, namely for \(| {B}_{z}| ={B}_{\max ,{I}_{c}}\approx 10\) mT (black and red arrow). The red and black solid line are guides to the eye, mutually symmetric upon reflection around B_z = 0. g Supercurrent rectification efficiency \(Q\equiv 2({I}_{c}^{+}-| {I}_{c}^{-}| )/({I}_{c}^{+}+| {I}_{c}^{-}| )\), plotted versus B_z. Q is maximal for \({B}_{z}={B}_{\max ,Q}\approx 35\) mT (arrow). Measurements in (c–g) were performed at 1.3 K. As discussed in the Supplementary Information, an offset of −2.5 mT and 0.17 μA has been removed from B_z and I_c, respectively.