Cooper pairs in non-centrosymmetric superconductors can acquire finite centre-of-mass momentum in the presence of an external magnetic field. Recent theory predicts that such finite-momentum pairing can lead to an asymmetric critical current, where a dissipationless supercurrent can flow along one direction but not in the opposite one. Here we report the discovery of a giant Josephson diode effect in Josephson junctions formed from a type-II Dirac semimetal, NiTe₂. A distinguishing feature is that the asymmetry in the critical current depends sensitively on the magnitude and direction of an applied magnetic field and achieves its maximum value when the magnetic field is perpendicular to the current and is of the order of just 10 mT. Moreover, the asymmetry changes sign several times with an increasing field. These characteristic features are accounted for by a model based on finite-momentum Cooper pairing that largely originates from the Zeeman shift of spin-helical topological surface states. The finite pairing momentum is further established, and its value determined, from the evolution of the interference pattern under an in-plane magnetic field. The observed giant magnitude of the asymmetry in critical current and the clear exposition of its underlying mechanism paves the way to build novel superconducting computing devices using the Josephson diode effect.

非中心对称超导体中的库珀对在存在外部磁场的情况下可以获得有限的质心动量。最近的理论预测，这种有限动量配对会导致不对称临界电流，其中无耗散的超电流可以沿一个方向流动，但不能沿相反方向流动。_{在这里，我们报告在由 II 型狄拉克半金属 NiTe 2}形成的约瑟夫森结中发现了巨大的约瑟夫森二极管效应. 一个显着的特点是临界电流的不对称性敏感地取决于所施加磁场的大小和方向，并且当磁场垂直于电流并且仅为 10 mT 的数量级时达到其最大值。此外，随着场的增加，不对称性会多次改变符号。这些特征由基于有限动量库珀配对的模型解释，该模型主要源于自旋螺旋拓扑表面状态的塞曼位移。从平面内磁场下干涉图案的演变进一步建立了有限配对动量，并确定了其值。