NMR Study of the Dynamics of 3He Impurities in the Proposed Supersolid State of Solid 4He

The dynamics of He-3 atoms in solid He-4 have been investigated by measuring the NMR relaxation times T-1 and T-2 in the region where a significant nonclassical rotational inertia fraction has been reported. For He-3 concentrations x(3) 16 and 24 ppm, changes are observed for both the spin-lattice relaxation time T-1 and the spin-spin relaxation time T-2 at the temperatures corresponding to the onset of the nonclassical rotational inertia fraction and, at lower temperatures, to the He-3-He-4 phase separation. The magnitudes of T-1 and T-2 at temperatures above the phase separation agree roughly with existing theory based on the tunneling of He-3 impurities in the elastic strain field due to isotopic mismatch. However, a distinct peak in T-1 and a less well-resolved feature in T-2 are observed near the reported nonclassical rotational inertia fraction onset temperature, in contrast to the temperature-independent relaxation times predicted by the tunneling theory.