Effect of hydrogen uptake and substrate orientation on the flux penetration in NbHx thin films

By absorbing various amounts of hydrogen in the same niobium sample we are able to change the local superconducting properties thus introducing quenched disorder in a controlled manner. Its effect on the magnetic flux penetration in NbHx thin films on A-plane (1 1 2-bar 0) and R-plane (1 1-bar 0 2) sapphire substrates is systematically investigated using a magneto-optical technique. With increasing hydrogen content, flux penetration patterns are observed to become more irregular. At high hydrogen concentrations non-superconducting inclusions are formed. The substrate orientation also has a strong influence on the observed behavior, revealing line-shaped avalanches at 4.2 K for A-plane substrates and a more continuous but spatially irregular behavior for R-plane substrates