Superfluidity of liquid ^3He in aerogel

用超声波测量方法研究了气凝胶中液态氦的超流动性。我们得到了以下结果。1.超声波光谱仪使用相敏检测的超声波光谱仪已与此赠款购买的接收器。该系统能够灵敏地测量声速。主要研究员，松本已转移到金泽大学，使我们不得不作出一个新的系统，并已完成它。气凝胶-He_4系统中的复声模式为了测试该系统，用液体He_4进行了10 MHz超声测量。我们观察到了气凝胶与液体之间的耦合运动所产生的复杂声模。一个重要的结果是，这种模式的声速是非常敏感的气凝胶密度。理论分析预测了两个复杂的声音模式和观察到的模式已被证明是对应的快速模式。这是第一次在正常和超流体相中观察到这种模式。观察到了大的吸收系数和没有由于转动-声子相互作用引起的吸收峰。这些结果已发表在Pysica B（如参考文献所示）。主要研究员松本于2000年4月从东京工业大学转到金泽大学。东京工业大学的核退磁制冷机已不能使用，因此金泽大学必须建造一台新的制冷机。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，以达到低于1 mK的温度，这是必要的研究液体He 3的超流动性。

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.