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

Abstract

The NMR spin-lattice relaxation data 1) for H in scandium metal solid solutions below 100 K have been reinterpreted in terms of local tunneling motion in two-well potentials rather than as 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 use distributions of A that broaden with increasing concentrations of H. For the local motion of H in Sc we find the sinusoidal barrier of height = 3200 K from inelastic neutron scattering 2), which gives the ground state tunnel splitting = 0.37 K. Then the coupling constants to electrons and phonons fitted to the spin relaxation are about the same as those for H in Nb 3), 4).