Electric field gradients probed by mu+SR in Sc and alpha-ScHx solid solutions

In Sc and alpha-ScHx below 40 K two mu(+) states are formed: a tunnelling state extending over two adjacent tetrahedral (T) interstices sharing one face in the ab-plane of the hcp host lattice and a static mu(+)-Sc-H configuration analog to the T-pair state formed by two H atoms across a Sc site along the crystalline c-axis. This explains perfectly the high transverse-field (TF) mu SR measurements at low temperature and allows a qualitative understanding of the temperature dependence. The modelling of the low TF measurements requires in addition the consideration of the electric field gradient (EFG) components acting on the Sc nuclei near the mu(+), i.e., of the radial EFG due to the mu(+) and of the axially symmetric crystal field. The magnetic field dependence of the anisotropic mu(+)SR relaxation rate is strongly influenced by the H-concentration in the solid solution system.