Sharma Nileema, Toole Matthew, McKenzie James, Ran Sheng, Liu Xiaolong
Department of Physics and Astronomy, University of Notre Dame, Notre Dame, IN, USA.
Stavropoulos Center for Complex Quantum Matter, University of Notre Dame, Notre Dame, IN, USA.
Nat Mater. 2025 Jul 22. doi: 10.1038/s41563-025-02290-y.
In a Josephson junction involving multiband superconductors, competition between interband and interjunction Josephson couplings gives rise to frustration and spatial disjunction of superfluid densities among superconducting condensates. Such frustrated coupling manifests as the quantum interference of Josephson currents from different tunnelling channels and becomes tunable if channel transparency can be varied. To explore these unconventional effects in the prototypical s-wave superconductor FeSe (ref. ), we use atomic-resolution scanned Josephson tunnelling microscopy for condensate-resolved imaging and junction tuning-capabilities unattainable in macroscopic Josephson devices with fixed characteristics. We quantitatively demonstrate frustrated Josephson tunnelling by examining two tunnelling inequalities. The relative transparency of two parallel tunnelling pathways is found tunable, revealing a tendency towards a 0-π transition with decreasing scanned Josephson tunnelling microscopy junction resistance. The simultaneous visualization of both superconducting condensates reveals anticorrelated superfluid modulations, highlighting the role of interband scattering. Our study establishes scanned Josephson tunnelling microscopy as a powerful tool enabling new research frontiers of multicondensate superconductivity.
在一个涉及多带超导体的约瑟夫森结中，带间和结间约瑟夫森耦合之间的竞争导致了超导凝聚体中超流密度的受挫和空间分离。这种受挫耦合表现为来自不同隧穿通道的约瑟夫森电流的量子干涉，并且如果通道透明度可以改变，它就变得可调谐。为了在典型的s波超导体FeSe（参考文献）中探索这些非常规效应，我们使用原子分辨率扫描约瑟夫森隧穿显微镜进行凝聚体分辨成像和结调谐，这是具有固定特性的宏观约瑟夫森器件所无法实现的。我们通过研究两个隧穿不等式定量地证明了受挫的约瑟夫森隧穿。发现两条平行隧穿路径的相对透明度是可调谐的，揭示了随着扫描约瑟夫森隧穿显微镜结电阻的降低向0-π转变的趋势。对两个超导凝聚体的同时可视化揭示了反相关的超流调制，突出了带间散射的作用。我们的研究将扫描约瑟夫森隧穿显微镜确立为一种强大的工具，能够开启多凝聚体超导性的新研究前沿。
