Chen Shaowen, Park Seunghyun, Vool Uri, Maksimovic Nikola, Broadway David A, Flaks Mykhailo, Zhou Tony X, Maletinsky Patrick, Stern Ady, Halperin Bertrand I, Yacoby Amir
Department of Physics, Harvard University, Cambridge, MA, 02138, USA.
Max Planck Institute for Chemical Physics of Solids, 01187, Dresden, Germany.
Nat Commun. 2024 Sep 14;15(1):8059. doi: 10.1038/s41467-024-52271-z.
Josephson junctions enable dissipation-less electrical current through metals and insulators below a critical current. Despite being central to quantum technology based on superconducting quantum bits and fundamental research into self-conjugate quasiparticles, the spatial distribution of super current flow at the junction and its predicted evolution with current bias and external magnetic field remain experimentally elusive. Revealing the hidden current flow, featureless in electrical resistance, helps understanding unconventional phenomena such as the nonreciprocal critical current, i.e., Josephson diode effect. Here we introduce a platform to visualize super current flow at the nanoscale. Utilizing a scanning magnetometer based on nitrogen vacancy centers in diamond, we uncover competing ground states electrically switchable within the zero-resistance regime. The competition results from the superconducting phase re-configuration induced by the Josephson current and kinetic inductance of thin-film superconductors. We further identify a new mechanism for the Josephson diode effect involving the Josephson current-induced phase. The nanoscale super current flow emerges as a new experimental observable for elucidating unconventional superconductivity, and optimizing quantum computation and energy-efficient devices.
约瑟夫森结能够使低于临界电流的电流无耗散地通过金属和绝缘体。尽管它对于基于超导量子比特的量子技术以及自共轭准粒子的基础研究至关重要，但结处超电流的空间分布及其随电流偏置和外部磁场的预测演化在实验上仍然难以捉摸。揭示在电阻中无特征的隐藏电流有助于理解诸如非互易临界电流（即约瑟夫森二极管效应）等非常规现象。在此，我们引入一个平台来可视化纳米尺度下的超电流。利用基于金刚石中氮空位中心的扫描磁力计，我们发现了在零电阻区域内可电切换的竞争基态。这种竞争源于约瑟夫森电流和薄膜超导体的动电感所引起的超导相重新配置。我们进一步确定了一种涉及约瑟夫森电流诱导相位的约瑟夫森二极管效应新机制。纳米尺度的超电流作为一种新的实验可观测量出现，用于阐明非常规超导性，并优化量子计算和节能设备。
