We compared liquid and solid 3 He-4 He mixtures at coexistence using NMR imaging of the density of 3 He and of the T2 relaxation time in the two phases. We find that above 1 K, 3 He atoms in a bcc solid are more mobile than in the superfluid liquid. This rapid motion, induced by vacancies, takes place on a microscopic scale and can be explained in terms of 3 He-vacancy attraction of quantum origin. We relate our observations to similar effects observed in Sn-Pb alloys.

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