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

在^3He；-4&gt；溶液中的相分离边界是理想的平坦表面。特别是在1mK以下，上相为P波超流体，理论上预测那里存在安德列夫散射。要观察它，液体必须冷却到弹道温度区域。我们制作了一种性能优良的换热器，在该换热器中，将细银和铂粉组合烧结成0.5 mm的厚度(有效表面积为350m^2)，在纯液体^3@He中获得了约170muK的最低温度。然后我们开发了一个由内径4 mm，厚度1 mm的银半球制成的黑体散热器。它的表面有一个直径为0.2 mm的小孔，它的轴线指向^3@He准粒子束以20度的小角度撞击边界表面。在散热器内部有两根半圆形振动丝，一根用来产生准粒子束，另一根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的自由面。对于有表面和无表面的情况，从黑体发射的能量通量与加热器振丝中施加的加热器功率成正比。然而，这两种情况下的斜坡之间有明显的区别。这一事实表明，量子Andreev反射明显存在于超流体^3@He B的自由面上。观察到的反射比预期的要小，但如果考虑孔口扩散散射的损失，则可以用准经典理论解释。孔口的形状是进行定量分析的重要因素。对于不同的长宽比和不同的孔口表面条件，计划进行进一步的实验。

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.