Benjamin Shank with Arnold Dahm

He3 Diffusion As a Probe of Delocalized Vacancies in HCP He4

Vacancies travel through He4 crystals by quantum tunneling. NMR will be used to measure the rate of vacancy assisted diffusion of isotropic He3 impurities through the HCP lattice of He4. The rate of this motion has been tested before, but experimental results vary. He3 atoms are used as probes because they are relatively light and electrically neutral; they do not create large distortions of the lattice. Diffusion is measured in the direction normal to planar magnetic field gradients induced in the sample. Measurements will be taken in three orthogonal directions to test for anisotropic diffusion. In particular, diffusion rates may differ along the c-axis and on the basal plane. After the orientation of the c-axis is determined, diffusion along the c-axis and in two orthogonal directions on the basal plane will be measured to test this hypothesis.