NMR Studies of 3He Impurities in 4He in the Proposed Supersolid Phase
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Preliminary results are reported for measurements of the NMR relaxation times of very dilute 3He in samples of solid 4He at low temperature, 0.25 K <T< 1.3 K. The results were obtained for carefully prepared samples with different 3He concentrations. The measurements of the spin-spin relaxation time, T 2, show several interesting features. A temperature independent plateau attributed to the exchange motional narrowing is observed down to the lowest temperature studied, and the observed variation of T 2 with 3He concentration favors the nonlinear theory suggested by Landesman. The best fit to the data is given by T 2 ∝ x 3 −1.89±0.1 rather than x 3 −1 . No evidence of an exchange-phonon bottleneck for the spin-lattice relaxation is seen down to 25 mK. The vacancy activation energy is determined to be 13.5±0.3 K for a sample with x 3=5×10−4 and molar volume 20.9 cm3.
KeywordsSupersolid NMR 3He–4He mixture Quantum defects
PACS67.60-g 67.80.bd 05.30-d 07.20.Mc