Study of the Impurity Effect in Superfluid Helim 3

通过测量气凝胶中超流中的第四声，研究了p波超流中的杂质效应。我们使用孔隙率分别为97.5%、98%和98.5%的气凝胶作为超流^3He的杂质，其杂质含量分别为2.5%、2%和1.5%。在第四个健全的实验中，我们发展了将气凝胶模制成电池的方法，用一种新设计的核退磁低温恒温器冷却^3He流体，这种低温恒温器是用高纯度的无氧铜（OFC）棒加工而成。在热处理之后，将核级安装在稀释制冷机中。在8T的高磁场中用稀释制冷机进行预冷，冷却至16mK，然后将核级磁性去磁至低场。在此基础上，我们获得了45 μK的最低温度，并在250 μK以下维持了一个多月。我们的研究结果表明：1.杂质的加入使超流密度和转变温度都降低。2.随着杂质的增加，这些温度都有系统地降低。结果表明，杂质对p波超流性的限制比s波超流性更大。我们在国际会议上发表了结果，并讨论了超流中的杂质效应。

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.