We review measurements of ⁴He near the superfluid transition in arrangements whereby an array of weak links couple relatively larger, more bulk- like ⁴He regions. In contrast to experiments which focus on the dependence of the superflow on the chemical potential difference across the links, these studies focus on the specific heat of both the weak links and that of the larger coupled regions, as well as the behavior of the superfluid fraction within the weak links. The data show unexpected results which reflect a very long range coupling as well as modification of the weak link itself due to the proximity to bulk-like helium. One finds that while the three-dimensional correlation length ξ(t), where t = |1 - T/T_λ|, is involved in these long-range effects, the distance over which these can be seen is of the order of 100 to 1000 times ξ(t). These results call into question our understanding of the meaning of the correlation length at a critical point as the 'range' over which information can propagate. These studies are the first to measure the thermodynamic properties of weak links for a critical system where fluctuations are important. They differ in essential ways with expectations from mean-field considerations. We compare results with other ⁴He measurements, with superconductors and the theoretical calculations of the Ising model.

中文翻译：

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通过邻近和弱链接耦合对临界系统中的巨大相关长度效应的回顾：⁴ He 接近超流体转变

我们回顾了⁴ He 在超流体过渡附近的测量结果，其中一组弱链接耦合相对更大、更像块状的⁴ He 区域。与侧重于超流对连接之间化学势差的依赖性的实验相比，这些研究侧重于弱连接和较大耦合区域的比热，以及超流体部分的行为薄弱环节内。数据显示了意想不到的结果，这反映了非常长的距离耦合以及由于接近体状氦而导致的弱链接本身的修改。人们发现，虽然三维相关长度 ξ(t)，其中 t = |1 - T/T _λ|, 与这些远距离效应有关，可以看到这些效应的距离约为 ξ(t) 的 100 到 1000 倍。这些结果质疑我们对临界点相关长度的含义的理解，即信息可以传播的“范围”。这些研究是第一个测量波动很重要的关键系统的薄弱环节的热力学特性的研究。它们在本质上与平均场考虑的期望不同。我们将结果与其他⁴ He 测量、超导体和 Ising 模型的理论计算进行了比较。