Tunneling and spin-lattice relaxation of hydrogen dissolved in scandium metal

Some published NMR spin-lattice relaxation data for H in ${\mathrm{ScH}}_{\mathit{x}}$ metal solid solutions below 100 K [Lichty et al., Phys. Rev. B 39, 2012 (1989)] have been reinterpreted in terms of local tunneling motion in two-well potentials rather than classical over-the-barrier hopping. The asymmetry A between the wells strongly influences the electron- and phonon-induced tunneling transition rates and also the intensity of the relaxation in the two-level system. The fit to the data uses distributions of A that broaden with increasing concentrations of H. For the local motion of H in Sc, we find the barrier ${\mathit{V}}_0$/${\mathit{k}}_{\mathit{B}}$≃3200 K, the ground-state tunnel splitting Δ${\mathit{E}}_{\mathit{T}0}$/${\mathit{k}}_{\mathit{B}}$≃0.37 K, and coupling constants to electrons and phonons that have the same orders of magnitude as those for H in Nb.