The Josephson Diode Effect in Junctions formed from 2D Van der Waals Metals

Recently we have discovered a non-reciprocal Josephson diode effect in several Josephson junctions, both lateral and vertical, formed from conventional superconducting electrodes (Nb, NbSe₂) separated by several non-superconducting metals including the 2D van der Waals Dirac semi-metal, NiTe₂[1]. We discuss a variety of other 2D metals that show a Josephson diode effect including WTe₂ [2], as well as those that do not show an effect such as MoTe₂. Each of these materials becoming superconducting by proximity to the conventional superconducting electrodes. The superconductivity can be sustained over long distances of, in some cases, up to ~1 micron. The critical supercurrent densities for current flowing in opposite directions within the junction are distinct and can vary by up to ~80%. The non-reciprocity is only observed in the presence of a small magnetic field oriented perpendicular to the supercurrent. For vertical Josephson junctions formed from WTe₂we show that the non-reciprocity depends on the orientation of the magnetic field with respect to the crystal structure of the WTe₂, proving thereby the intrinsic origin of the Josephson diode effect. Such an effect could have important applications as a novel magnetic field detector at cryogenic temperatures, for example, to “read” magnetic domain walls in a cryogenic racetrack memory^*.<br/><b>^*</b>Funded through an European Research Council Advanced Grant “SUPERMINT” (2022-2027).<br/><br/>[1] B. Pal<i> et al.</i>, "Josephson diode effect from Cooper pair momentum in a topological semimetal," <i>Nat. Phys., </i>vol. 18, pp. 1228-1233, 2022.<br/>[2] J.-K. Kim, K.-R. Jeon, P. K. Sivakumar, J. Jeon, C. Koerner, G. Woltersdorf, and S. S. P. Parkin, "Intrinsic supercurrent non-reciprocity coupled to the crystal structure of a van der Waals Josephson barrier," <i>arXiv:2303.13049, </i>2023.