The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel.
Department of Materials Science & Metallurgy, University of Cambridge, Cambridge, CB3 0FS, United Kingdom.
Nat Commun. 2023 Mar 24;14(1):1630. doi: 10.1038/s41467-023-37294-2.
The interplay between magnetism and superconductivity can lead to unconventional proximity and Josephson effects. A related phenomenon that has recently attracted considerable attention is the superconducting diode effect, in which a nonreciprocal critical current emerges. Although superconducting diodes based on superconductor/ferromagnet (S/F) bilayers were demonstrated more than a decade ago, the precise underlying mechanism remains unclear. While not formally linked to this effect, the Fulde-Ferrell-Larkin-Ovchinikov (FFLO) state is a plausible mechanism due to the twofold rotational symmetry breaking caused by the finite center-of-mass-momentum of the Cooper pairs. Here, we directly observe asymmetric vortex dynamics that uncover the mechanism behind the superconducting vortex diode effect in Nb/EuS (S/F) bilayers. Based on our nanoscale SQUID-on-tip (SOT) microscope and supported by in-situ transport measurements, we propose a theoretical model that captures our key results. The key conclusion of our model is that screening currents induced by the stray fields from the F layer are responsible for the measured nonreciprocal critical current. Thus, we determine the origin of the vortex diode effect, which builds a foundation for new device concepts.
磁性和超导性之间的相互作用会导致非常规的近邻和约瑟夫森效应。最近，一种相关的现象引起了相当多的关注，即超导二极管效应，其中会出现非互易临界电流。虽然基于超导/铁磁体（S/F）双层结构的超导二极管在十多年前就已经得到了证明，但确切的潜在机制仍不清楚。虽然与该效应没有正式联系，但富勒-费雷尔-拉金-奥夫钦尼科夫（FFLO）态是一个合理的机制，因为库珀对的有限质心动量会导致两倍的旋转对称性破坏。在这里，我们直接观察到非对称涡旋动力学，揭示了 Nb/EuS（S/F）双层结构中超导涡旋二极管效应背后的机制。基于我们的纳米级超导量子干涉仪尖端（SOT）显微镜，并结合原位传输测量，我们提出了一个能够捕捉到我们关键结果的理论模型。该模型的关键结论是，来自 F 层的杂散场感应的屏蔽电流是导致测量到的非互易临界电流的原因。因此，我们确定了超导二极管效应的起源，为新的器件概念奠定了基础。
