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

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: YBa2C u3O7-x (YBCO) films and YBa2Cu3O7-x/PrBa2Cu3O7 (YBCO/PBCO) superlattices. I n 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 th ickness of 1000 Angstrom. The analysis is presented in terms of depression of the critical temperature (T-c) and modification of the crystalline struc ture using X ray refinement technique. Single films show a systematic incre ase in the c-lattice parameter upon irradiation, which is not observed in t hin one unit cell YBCO layers in superlattice structures. However, T-c depr ession 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 p ersistent photoconductivity, indicating that defects are related to oxygen displacements in the Cu-O chains. (C) 2000 American Institute of Physics. [ S0003-6951(00)05322-5].