Structural and electrical properties of PrBa2Cu3-xGaxO7 (x=0.2) thin films and [(PrBa2Cu3-xGaxO7)M/(YBa2Cu3O7)N]P superlattices grown by pulsed laser deposition

The low temperature resistivity (T<200 K) of PrBa2Cu3-xGaxO7 (x=0.2) thin films grown by pulsed laser deposition follows the Mott variable range hopping law. The positive lattice mismatch to SrTiO3 (Δa/a=+0.15%) leads to alternately strained pseudomorphic superlattices with YBa2Cu3O7, when the elementary layer is ultra-thin (≤5 nm). Chemical diffusion of gallium in YBa2Cu3O7/PrBa2Cu3-xGaxO7 heterostructures is neither detected from the refinement calculations of the XRD spectra nor from SIMS profile analysis. The Tc lowering of the superlattices is explained in terms of charge transfer effect. The shortest period superlattices without Josephson coupling between the YBa2Cu3O7 layers (M>3, N≤4) show Kosterlitz-Thouless bidimensional fluctuations due to the strong anisotropy of the structure. (orig.)