Strong pinning linear defects formed at the coherent growth transition of pulsed-laser-deposited (formula presented) films

Linear defects are important pinning sites for vortices in high-temperature superconductors. In (formula presented) thin films, the linear defects responsible for high critical currents are threading dislocations formed near the substrate interface. Investigating the first stages of growth of pulsed-lased-deposited (formula presented) on single terminated (100) (formula presented) substrates, we study the genesis of these dislocations. We find that the formation of linear defects occurs above a certain critical layer thickness at which a coherent growth transition takes place. Coherent islands are formed, surrounded by highly strained trenches. These trenches facilitate the formation of dislocation half-loops. Such half-loops relieve the misfit strain and form misfit and threading dislocations. The number of threading dislocations thus depends on the island density. This model explains both the short-range lateral order of the threading dislocations and their decreasing density at elevated substrate temperatures.