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Andreev refrlection and proximity effect at the phase boundary of ^3He-^4He mixutures

^3He-^4He 混合物相界的 Andreev 反射和邻近效应

基本信息

批准号：
08454091
负责人：
ISHIMOTO Hidehiko
金额：
$ 4.29万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08454091/
关键词：
Andreev reflection Superfluid ^3He ^3He-^4He mixture proximity effect quasiparticle blackbody radiator quasihole vibrating wire ^3He-^4He混合液 vibrating wire ク-パ-対 P波

项目摘要

A phase separated boundary in the ^3He^<-4> solution is an ideally flat surface. Especially below 1 mK, the upper phase is a P-wave superfluid and the Andreev scattering is theoretically predicted to exist there. To observe it, the liquid has to be cooled down to the ballistic temperature region. We made an excellent heat exchanger, in which a combination of fine silver 2 and platinum powder is sintered to have a thickness of 0.5 mm (effective surface area 350m^2) , resulting into the lowest temperature of about 170muK in pure liquid ^3@He. We then developed a blackbody radiator made of a silver hemisphere with 4 mm in inner diameter and 1 mm in thickness. On its surface there exists an orifice of 0.2 mm in diameter, whose axis is oriented for the ^3@He quasiparticle beam to hit the boundary surface at a small angle of 20 degree. Inside the radiator two semicircular vibrating wires, one to produce a quasiparticle beam and the other to measure the quasiparticle density there. To test the system, the free surface of superfluid ^3@He B was used. The emitted energy flux from the blackbody is proportional to an applied heater power in the heater vibrating wire for the cases with and without the surface. However there is a clear difference between the slopes for both cases. This fact indicates that the quantum Andreev reflection clearly exists at the free surface of superfluid ^3@He B.The obseved reflection rare is smaller than expected but can be explained with a quasiclassical theory if we take into account the loss due to the diffuse scattering at the orifice. The shape of the orifice is found very important to make a quatitative analysis. Further experiments are planned for various aspect ratios and for the different surface conditions of the orifice.

^3He^溶液中的相分离边界<-4>是一个理想的平坦表面。特别是在1 mK以下，上层相是P波超流体，理论上预测那里存在Andreev散射。为了观察它，液体必须冷却到弹道温度区域。我们制作了一个很好的热交换器，其中细银2和铂粉末的组合被烧结到具有0.5 mm的厚度（有效表面积350 m^2），导致在纯液体^3@He中的最低温度约为170 μ K。然后，我们开发了一个黑体辐射器制成的银半球与4毫米的内径和1毫米的厚度。在其表面上有一个直径为0.2 mm的小孔，小孔的轴向使^3@He准粒子束以20 °的小角度撞击边界面。在辐射器内部有两个半圆形的振弦，一个用来产生准粒子束，另一个用来测量那里的准粒子密度。为了测试该系统，使用了超流体^3@He B的自由表面。对于有表面和没有表面的情况，黑体发射的能通量与加热器振动线中施加的加热器功率成正比。然而，两种情况下的斜率之间存在明显差异。这一事实表明，量子Andreev反射明显存在于超流^3@He B的自由表面。所观察到的反射率比预期的要小，但如果我们考虑到由于孔处的漫散射引起的损失，可以用准经典理论来解释。发现小孔的形状对定量分析是很重要的。进一步的实验计划为各种长宽比和不同的表面条件的孔。