A gas junction In superconductors, electrons form a macroscopic wave function that has a definite phase. If two superconductors with different wave function phases are placed in contact with each other through an insulating link, a current will flow through this so-called Josephson's junction without any external voltage. Luick et al. and Kwon et al. observed an analogous phenomenon in a setup that involved two reservoirs of superfluid Fermi gases. Both groups measured the so-called current-phase relation: the dependence of the magnitude of the current on the relative phase. By tuning an external magnetic field, they were able to study how the interactions between fermions affected the nature of the superfluid state. Science, this issue p. 89, p. 84 A Josephson junction was created between two Fermi gas superfluids. The direct-current (dc) Josephson effect provides a phase-sensitive tool for investigating superfluid order parameters. We report on the observation of dc Josephson supercurrents in strongly interacting fermionic superfluids across a tunneling barrier in the absence of any applied potential difference. For sufficiently strong barriers, we observed a sinusoidal current-phase relation, in agreement with Josephson’s seminal prediction. We mapped out the zero-resistance state and its breakdown as a function of junction parameters, extracting the Josephson critical current behavior. By comparing our results with an analytic model, we determined the pair condensate fraction throughout the Bardeen-Cooper-Schrieffer–Bose-Einstein condensation crossover. Our work suggests that coherent Josephson transport may be used to pin down superfluid order parameters in diverse atomic systems, even in the presence of strong correlations.

中文翻译：

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来自直流约瑟夫森超流的强相关超流阶参数

气体结 在超导体中，电子形成具有确定相位的宏观波函数。如果两个具有不同波函数相位的超导体通过绝缘连接相互接触，电流将流过这个所谓的约瑟夫森结，而没有任何外部电压。卢克等人。和权等人。在涉及两个超流体费米气体库的设置中观察到类似的现象。两组都测量了所谓的电流-相位关系：电流幅度对相对相位的依赖性。通过调整外部磁场，他们能够研究费米子之间的相互作用如何影响超流体状态的性质。科学，这个问题 p。89，第。84 在两种费米气体超流体之间形成了约瑟夫森结。直流 (dc) 约瑟夫森效应为研究超流体序参数提供了一种相敏工具。我们报告了在没有任何施加电位差的情况下，在穿过隧道势垒的强相互作用费米子超流体中观察到直流约瑟夫森超电流。对于足够强的障碍，我们观察到正弦电流-相位关系，与约瑟夫森的开创性预测一致。我们绘制了零电阻状态及其作为结参数函数的击穿，提取了约瑟夫森临界电流行为。通过将我们的结果与分析模型进行比较，我们确定了整个 Bardeen-Cooper-Schrieffer-Bose-Einstein 冷凝交叉过程中的成对冷凝分数。