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

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