Positron trapping in a co-evaporation epitaxial superconducting thin film YBa2Cu3O7−x

The positron lifetime as a function of implantation energy was measured on a co-evaporation epitaxial superconducting thin film YBa2Cu3O7-x by using a pulsed low energy positron beam system in Munich. Detailed analysis shows that (i) here are both shallow and deep trapping centers in the film, (ii) the defects concerning the long-lived lifetime, tau(2), have an enlargement trend at lower temperature and may become one of the effective flux pinning centers. The variation of the mean lifetime with temperature indicates that almost all positrons escape from the shallow trapping centers at a temperature higher than the room temperature. At temperatures higher than 373 K, an annealing effect should be considered.