Study of the Impurity Effect in Superfluid Helim 3

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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.