Simultaneous measurement of torsional oscillations and NMR of very dilute ^{3}He in solid ^{4}He

概要

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We have investigated the NMR properties of dilute 3He impurities in solid 4He contained in a torsional oscillator (TO) by the simultaneous measurement of the NMR and the torsional oscillator response of the so-called supersolid 4He. From measurements on samples with one hundred to a few hundred parts per million (ppm) of 3He, we have found three different states of 3He. The first is the homogeneously distributed isolated 3He atom in a solid matrix of 4He. The second is the 3He cluster in a homogeneous 4He matrix, which appears below the phase-separation temperature of a solid mixture. The third is the 3He cluster in some nonuniform part of a 4He crystal. We find that 3He atoms contained in the third component remain in a nearby location even above the phase-separation temperature. Based on the fact that even a ppm of 3He affects the supersolid response in a TO below and above the phase-separation temperature, we propose that the nonuniform part of a crystal that holds the third type of 3He and thus has a higher local concentration of 3He plays an important role in the supersolid phenomenon in a TO.