Study of the Impurity Effect in Superfluid Helim 3

通过测量气凝胶中超流体中的第四声，研究了p波超流态中的杂质效应。我们用孔隙率为97.5%、98%和98.5%的气凝胶作为杂质，分别为2.5%、2%和1.5%来制备超流体~3He。在第四个声学实验中，我们发展了气凝胶模塑成细胞的方法。用一种新设计的核退磁低温恒温器来冷却~3He液体，该恒温器是由高纯度的无氧铜棒加工而成的。核反应堆安装在经过热处理后的稀释冰箱中。用稀释制冷机在8T的强磁场中预冷至16mK，然后将核级绝热退磁到低场。在此之后，我们得到了最低温度为45μK，并将温度保持在250μK以下一个月以上。我们的研究结果如下：1.加入杂质后，超流体密度和转变温度都降低了。2.随着杂质的增加，超流体密度和转变温度都有系统地降低。结果表明，杂质对p波超流的限制比S波的要大。我们在国际会议上发表了这一结果，并讨论了超流体中的杂质效应。我们还在科学期刊上发表了这些结果。

We have investigated the impurity effect in the p-wave superfluidity by measuring the fourth sound in superfluid in aerogels. We utilized aerogels with porosities of 97.5, 98 and 98.5 % as impurities of 2.5, 2 and 1.5 %, respectively, for superfluid ^3He. For the fourth sound experiment we have developed the mold method of aerogel into a cell.The ^3He fluid was cooled with a new design of a nuclear demagnetization cryostat which was machined from an oxygen free copper (OFC) rod with high purity. The nuclear stage was mounted in a dilution refrigerator after a heat treatment. Precooling was performed with the dilution refrigerator down to 16 mK in a high magnetic field of 8 T and then the nuclear stage was demagnetized adiabatically to low fields. After that we obtained the lowest temperature of 45 μK and maintained temperature below 250 μK over one month.We have found results in the present study as follows:1.Both the superfluid density and the transition temperature of are reduced if impurities are applied.2.These are decreased systematically with increasing impurities.The results suggest that impurities more restrict the p-wave superfluidity than s-wave one.We have presented the results in international meetings and discussed the impurity effect in the superfluid We have also published the results in scientific journals.