Superconductivity in YBa/sub 2/Cu/sub 3/O/sub 7//PrBa/sub 2/Cu/sub 3/O/sub 7/ superlattices

Abstract

High-quality YBa/sub 2/Cu/sub 3/O/sub 7//PrBa/sub 2/Cu/sub 3/O/sub 7/ superlattices with desired thicknesses of each component were fabricated by laser deposition. Superconductivity was studied by varying both YBa/sub 2/Cu/sub 3/O/sub 7/ and PrBa/sub 2/Cu/sub 3/O/sub 7/ layer thicknesses. The results indicate that an isolated single unit cell YBa/sub 2/Cu/sub 3/O/sub 7/ layer (nominal thickness of 12 AA) is superconducting. The increase of T/sub c/ from the lower value of a single unit cell layer to 90 K in thick films and the enhancement of T/sub c/ for a given thickness of YBa/sub 2/Cu/sub 3/O/sub 7/ when the PrBa/sub 2/Cu/sub 3/O/sub 7/ layers decreased to less than approximately 30 AA 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 YBa/sub 2/Cu/sub 3/O/sub 7/ 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 YBa/sub 2/Cu/sub 3/O/sub 7/ films.