Finite-size Scaling of Four Helium Near the Superfluid Transition and Two-Dimensional Behavior of Three Helium in Four Helium Films

液氦在低温下表现出许多有趣的性质。有些是这种量子流体独有的，另一些是其他系统常见的，但在氦中可以更精确地观察到。他们一直在研究超流体在极限转变时的临界行为，在这种极限下，氦被限制在如此小的维度上，以至于它不再表现为三维系统。他们设计了一种将氦限制在两个间隔良好的硅片之间的技术。他们首次报告了超流体密度的测量，在这种密度中，当一个人接近超流体转变时，氦偏离了三维行为，然后跨越到二维。他们建议在下一个资金期继续进行这些调查，并开始测量热容量。这些数据将为有限尺寸标度理论和维度交叉提供严格的测试。在低温下，他们研究了以~3He为杂质的~4He近单层膜的超流跃迁。他们报告说，观察到这些薄膜向超流体状态的转变分两个步骤进行。他们将此解释为3He表面态形成的标志。他们建议继续进行这些测量，以研究与3He的相变和流体力学质量相关的其他现象。

Liquid helium displays a number of interesting properties at low temperatures. Some are unique to this quantum fluid, others are common to other systems, but observable with a higher degree of precision in helium. They have been studying critical behavior at the superfluid transition in the limit where helium is confined to such small dimensions that it no longer behaves as a three dimensional system. They have devised a technique for confining the helium between two well-spaced silicon wafers. They report first measurements of the superfluid density in which, as one approaches the superfluid transition, the helium deviates from three-dimensional behavior and then crosses over into two dimensions. They propose to continue these investigations for the next funding period as well as to start measurements of heat capacity. These data will provide stringent tests of finite-size scaling theories and dimensionality crossover. At low temperatures they have studied the superfluid transiton of near-monolayer films of 4He with 3He as an impurity. They report the observation that the transition of these films into the superfluid state takes place in two steps. They interpret this as a signature of the formation of the surface state for 3He. They propose to continue with these measurements to study other phenomena associated with the phase transition and the hydrodynamic mass of 3He.