Positron annihilation in the epitaxial superconducting thin-film GdBa2Cu3O7- delta studied by using a pulsed positron beam.

Abstract

The positron lifetime as a function of implantation energy was measured on the epitaxial superconducting thin film GdBa2Cu3O7-delta at different temperatures. The coexistence of both shallow and deep positron trapping centers was observed in the film. The shallow trapping centers include the screw dislocations and twin boundaries. The binding energy of the shallow trapping centers was estimated to be 56 +/- 12 meV. The deep trapping centers are assigned the cation vacancies, especially barium vacancies. On the surface of the sample there are macroscopic free volume holes in which positronium could be formed.