Superfluidity of liquid ^3He in aerogel

利用超声测量技术研究了气凝胶中He液体的超流动性。我们得到了以下结果。超声光谱仪采用相敏检测的超声光谱仪已由本基金购买的接收器制成。该系统能够灵敏地测量声速。主要研究员Matsumoto已经搬到了金泽大学，所以我们必须制作一个新的系统，并且已经完成了。气凝胶-He4系统的复杂声音模式为了对该系统进行测试，采用10mhz超声对液态He4进行了测量。由于气凝胶和液体之间的耦合运动，在该系统中观察到复杂的声模。一个重要的结果是，这种模式的声速对气凝胶密度极为敏感。理论分析预测了两种复声模态，观测到的模态与快模态相对应。这是第一次在正常和超流体阶段都观察到这种模式。由于罗顿-声子相互作用，观察到吸收系数大且无吸收峰。这些结果已经发表在《物理学B》上（如参考文献所示）。主要研究员松本于2000年4月从东京工业大学跳槽到金泽大学。在东京工业大学不能再使用核消磁冰箱，只能在金泽大学建造新的冰箱。我们一直在努力建造核制冷机，主要部件已经完成。我们继续改进它，使其温度低于1 mK，这是研究液体He3超流动性所必需的。

Ultrasound measurement has been used to study super fluidity of liquid He in aerogel. We obtained the following results.1. Ultrasound spectrometer Ultrasound spectrometer using Phase Sensitive Detection has been made with a receiver purchased by this grant. This system enables to measure sound velocity sensitively. Main researcher, Matsumoto has moved to Kanazawa University so that we had to make a new system and has completed it.2. Complex sound mode in aerogel-He4 system For the test of the system, 10 MHz Ultrasound measurement has been done with liquid He4. We have observed complex sound mode in this system due to coupled motion between aerogel and liquid. An important result is that the sound velocity of this mode is extremely sensitive to the aerogel density. Theoretical analysis predicts the two complex sound modes and the observed mode has been shown to correspond to the fast mode. This is the first that this mode was observed in both normal and super fluid phase. Large absorption coefficient and no absorption peak due to Roton-Phonon interaction have been observed. These results have been published in Pysica B (as shown in the reference).3. Nuclear demagnetization refrigerator The main researcher, Matsumoto has move to Kanazawa University from Tokyo Institute of Technology in April 2000. We could not use nuclear demagnetizatio refrigerator in Tokyo Institute of Technology any more so that a new refrigerator had to be constructed at Kanazawa University. We have been trying to build nuclear refrigerator and main components have been completed. We continue improving it to achieve temperature below 1 mK which is necessary to study super fluidity of liquid He3.