High quality YBa2Cu3O7/PrBa2Cu3O7 superlattices with desired thickness of each component were fabricated by laser deposition. Superconductivity was studied by varying both YBa2Cu3O7 and PrBa2Cu3O7 layer thicknesses. The results indicated that an isolated single unit cell YBa2Cu3O7 layer (nominal thickness of 12 angstrom) 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 PrBa2Cu3O7 layers decreased to less than approximately 30 angstrom could be attributed to the interlayer coupling effect. Superconducting transitions of superlattices in applied magnetic fields 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 YBa2Cu3O7 layers, similar results to vortex-antivortex pair phase transition was observed by measuring the temperature dependence of resistance, magnetoresistance, and I-V curves, indicating a strong two dimensional behavior in very thin YBa2Cu3O7 films.
