Critical temperature depression and persistent photoconductivity in ion irradiated YBa2Cu3O7-x films and YBa2Cu3O7-x/PrBa2Cu3O7 superlattices

Abstract

We have studied the effect of He+ irradiation with doses in the range 10(12)-2x10(15) cm(-2) on two high-temperature superconducting structures: YBa2Cu3O7-x (YBCO) films and YBa2Cu3O7-x/PrBa2Cu3O7 (YBCO/PBCO) superlattices. In particular we have focused on superlattices [YBCON/PBCOM](1000 Angstrom) with N=1, 8 unit cells of YBCO, and M=5 unit cells of PBCO, with a total thickness of 1000 Angstrom. The analysis is presented in terms of depression of the critical temperature (T-c) and modification of the crystalline structure using X ray refinement technique. Single films show a systematic increase in the c-lattice parameter upon irradiation, which is not observed in thin one unit cell YBCO layers in superlattice structures. However, T-c depression resulting from irradiation is deeper in superlattices. These results are explained considering the strained nature of the as-grown [YBCON/PBCO5](1000 Angstrom) superlattices with low values of N. Both structures show persistent photoconductivity, indicating that defects are related to oxygen displacements in the Cu-O chains.