Pinning centres in YBa₂Cu₃O_{7- delta} films

Pinning centers in epitaxial YBa2Cu3O 7- delta films have been investigated by scanning tunneling microscopy and transport studies. An astonishing surface morphology has been found which includes a high density approximately=109 cm-2 of screw dislocations and nanometer-sized holes. The density of screw dislocations can be controlled by varying the growth conditions of the YBa 2Cu3O7- delta films, allowing correlations between critical currents and screw dislocation density to be investigated. Films with higher screw dislocation densities are observed to have higher critical current densities and a slower drop of Jc(H).