Lattice Relaxation of 4He with 3He Impurities: NMR Studies

Measurements of the He-3 nuclear spin relaxation times of dilute He-3 impurities in solid He-4 have been used to explore the unusual dynamics of solid 4He at low temperatures. The He-3 impurities move through the lattice by quantum mechanical exchange with neighboring He-4 atoms. Because of the larger zero point motion of the He-3 atoms, there is an appreciable lattice distortion that accompanies the tunneling He-3 atom and the tunneling motion depends on the elastic properties of the He-4 lattice. This motion modulates the He-3-He-3 nuclear dipoledipole interactions and thus determines the NMR relaxation rates. We compare the observed temperature dependence of the NMR relaxation rates with that expected from the measurements of the shear modulus by Syshchenko et al.