Neutron reflection from the surface of a liquid 4 He- 3 He mixture
Neutron reflection from the surface of a liquid 4 He- 3 He mixture
复制标题
液体 4 He- 3 He 混合物表面的中子反射
DOI：
10.1088/1742-6596/400/1/012033
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
Kirichek O
中科院分区：
文献类型：
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作者：
Kirichek O
我们利用超低温下液体表面的中子反射来研究液氦的表面性质。我们测量了从商业纯4 He（0.3 ppm的3 He杂质）和3 He-4 He混合物的自由表面的中子散射，3 He浓度为0.5%，温度范围从340 mK到2.2 K。我们比较了不同温度下的反射中子强度，并拟合了描述收集到的数据的模型。该数据被描述为一个扩散的3 He层的体积4 He液体表面上的几百埃厚。即使在高温下（102 K），在液体表面附近也有3个He原子的浓度增加。分布随温度变化不大。在低温下，中子吸收显著增加，这可能是形成Andreev态的指示。然而，曲线的形状并没有很大的变化，这似乎表明由Andreev态的3个He原子形成的层非常薄，大约10 μ m。基于中子反射计的实验方法为量子流体和固体的表面和界面的研究开辟了新的机会。
We have used neutron reflection from the liquid surface at ultra-low temperatures to study the surface properties of liquid helium. We measured neutron scattering from the free surfaces of commercially pure 4 He (0.3 ppm of 3 He impurities) and of a 3 He-4 He mixture with a 3 He concentration of 0.5% for temperatures in the range from 340mK to 2.2 K We compare the reflected neutron intensity for different temperatures and we fit a model that describes the collected data. The data are described well by a diffusive 3 He layer of a few hundred Angstrom thickness on the bulk 4 He liquid surface. Even at high temperatures (∼ 2K) there is an increased concentration of 3 He atoms near the liquid surface. The distribution does not change very much with temperature. At low temperatures the neutron absorption increases significantly, which might be an indication of the formation of Andreev states. However, the shapes of the curves do not change very much which seems to suggest that the layer formed by the 3 He atoms in Andreev states is very thin∼ 10Å. The experimental method, based on neutron reflectometry, opens up new opportunities for the study of the surfaces and interfaces of quantum fluids and solids.