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Study of Phase Transition of Superfluid Helium 3 in sub micrometer Space

亚微米空间超流氦3相变研究

基本信息

批准号：
10640352
负责人：
ISHIKAWA Osamu
金额：
$ 2.11万
依托单位：
OSAKA CITY UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10640352/
关键词：
Superfluid Helium 3 Phase Transition Anisotropic Superfluid Slab Geometry Coherence Length Size Effect Nuclear Magnetic Resonance Thin Helium 4 layers ヘリウム3 超流動異方性秩序パラメータサブミリケルビン

项目摘要

It became clear that the boundary condition of ^3He quasi particles at the surface had a great effect on the stability of superfluid phases by our experimental study on superfluid ^3He in 0.8 μm slab geometry. The anisotropy of ^3He superfluid state appears in real space and this anisotropy competes with the anisotropy of sample cell. As a result it is expected that we can observe the particular phase transition between superfluid states (A-B phase transition) and the suppression of the superfluid transition temperature when we put liquid ^3He in a cell whose size is close to the coherence length. The coherence length varies depending on pressures, the lower pressure, the longer coherence length. From this point of view the above expectation becomes more obvious at lower pressures.In our study, we developed the high Q-value tuned circuit for NMR detection with the low temperature amplifier to get the enough S/N ratio. We observed the lower A-B phase transition temperatures than those in 1.1 μm slab geometry at all pressures and also observed the large suppression of superfluid transition temperature. These were enhanced at lower pressures as expected and no A-B transition occurred lower than about 2 bar. The critical thickness well explained A-B phase transition phenomena at both slab geometries. Surprisingly the A-B phase transition temperature became higher when we put a few ^4He layers on the boundary surface. The superfluidity of thin ^4He layer seems to change the boundary condition for ^3He quasi particle and to lift A-B transition temperature. All the theoretical arguments, however, showed the opposite result so far. We need new theoretical work to discuss about our results.

通过我们对 0.8 μm 板片几何形状中超流^3He 的实验研究表明，^3He 准粒子在表面的边界条件对超流相的稳定性有很大影响。 ^3He超流态的各向异性出现在实空间中，并且这种各向异性与样品单元的各向异性相竞争。因此，当我们将液体^3He放入尺寸接近相干长度的晶胞中时，我们预计可以观察到超流态之间的特定相变（A-B相变）以及超流相变温度的抑制。相干长度根据压力而变化，压力越低，相干长度越长。从这个角度来看，上述期望在较低压力下变得更加明显。在我们的研究中，我们开发了用于核磁共振检测的高Q值调谐电路，并带有低温放大器以获得足够的信噪比。我们观察到在所有压力下 A-B 相变温度均低于 1.1 μm 板几何形状，并且还观察到超流体转变温度的大幅抑制。正如预期的那样，这些在较低压力下得到增强，并且在低于约 2 bar 的压力下没有发生 A-B 转变。临界厚度很好地解释了两种板坯几何形状的 A-B 相变现象。令人惊讶的是，当我们在界面上放置一些 ^4He 层时，A-B 相变温度变得更高。 ^4He薄层的超流性似乎改变了^3He准粒子的边界条件并提高了A-B转变温度。然而，迄今为止所有的理论论证都显示出相反的结果。我们需要新的理论工作来讨论我们的结果。