FORMATION OF ARTIFICIALLY-LAYERED HIGH-TEMPERATURE SUPERCONDUCTORS USING PULSED-LASER DEPOSITION

Superlattice structures, consisting of SrCuO2, (Ca,Sr)CuO2, and BaCuO2 layers in the tetragonal, 'infinite layer' crystal structure, have be en grown by pulsed-laser deposition (PLD). Superlattice chemical modul ation is observed for structures with component layers as thin as a si ngle unit cell (similar to 3.4 Angstrom), indicating that unit-cell co ntrol of (Ca,Sr)CuO2 growth is possible using conventional pulsed-lase r deposition over a wide oxygen pressure regime. X-ray diffraction int ensity oscillations, due to the finite thickness of the film, indicate that these films are extremely flat with a thickness variation of onl y similar to 20 Angstrom over a length scale of several thousand angst roms. Using the constraint of epitaxy to grow metastable cuprates in t he infinite layer structure, novel high-temperature superconducting st ructural families have been formed. In particular, epitaxially-stabili zed (Ca,Sr)CuO2/BaCuO2 superlattices, grown by sequentially depositing on lattice-matched (100) SrTiO3 from BaCuO2 and (Ca,Sr)CuO2 ablation targets in a PLD system, show metallic conductivity and superconductiv ity at T-c(onset) similar to 70 K. These results show that pulsed-lase r deposition and epitaxial stabilization have been used to effectively 'engineer' artificially-layered thin-film materials.