Superconductivity in YBa2Cu3O7/PrBa2Cu3 O7 superlattices

High-quality YBa₂Cu₃O₇/PrBa₂ Cu₃O₇ superlattices with desired thicknesses of each component were fabricated by laser deposition. Superconductivity was studied by varying both YBa₂Cu₃O₇ and PrBa₂Cu₃O₇ layer thicknesses. The results indicate that an isolated single unit cell YBa₂Cu₃O₇ layer (nominal thickness of 12 Å) is superconducting. The increase of T_c from the lower value of a single unit cell layer to 90 K in thick films and the enhancement of T_c for a given thickness of YBa₂Cu₃O₇ when the PrBa₂Cu ₃O₇ layers decreased to less than ~30 Å could be attributed to the interlayer coupling effect. Superconducting transitions of superlattices in an applied magnetic field were studied. The interlayer coupling effect on vortices can be seen by comparing the transition curves in high magnetic fields of thick film, ultrathin film, and superlattice. For the samples with very thin YBa₂Cu₃ O₇ layers, similar results to vortex-antivortex pair phase transition were observed by measuring the temperature dependence of resistance, magnetoresistance, and I-V curves, indicating strong two-dimensional behavior in very thin YBa₂Cu₃O₇ films