Search for Superfluid Helium-3 in Aerogel by Fourth Sound Technique

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In this research, we studied Superfluid Helium-3 in porous silica aerogel by Fourth Sound technique. We used three aerogel samples which have different density, one is 1% (which is corresponding to the porosity 99%), another is 1.5% (corresponding to 98.5%), the other is 2% (99%). Two of the three aerogel samples were grown inside the sintered silver powder typically 100 micrometer diameter to avoid vibration of the aerogel itself. The aerogels were made by Professor Norbert Mulders in University of Delaware. We used Fourth Sound technique to measure. We get superfluid density of Helium-3 from a measured sound velocity of Fourth Sound, which resonating in the sample cavity. The temperature dependence of the superfluid density gives us transition temperature.We measured superfluid density at several pressures between 2.7 bar and 18 bar. At all pressures, the superfluid transition temperaure is suppressed from the bulk one, because aerogel skeleton breaks Cooper pairs of superfluid helium-3. The transition temperature is more suppressed in higher density aerogel. The aerogel-density dependence of the transition temperature can be explained by a theory of Abrikosov and Gor'kov for superconductivity including magnetic impurities. Our result agrees quantitatively with A-G theory, but this does not agree with foreign groups. Regarding superfluid density, our results also can be explained by A-G theory, but other groups not The difference between our results and other group's results is not understood now. Further study is necessary.