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 been grown by pulsed-laser deposition (PLD). Superlattice chemical modulation is observed for structures with component layers as thin as a single unit cell (∼ 3.4 Å), indicating that unit-cell control of (Ca,Sr)CuO2 growth is possible using conventional pulsed-laser deposition over a wide oxygen pressure regime. X-ray diffraction intensity oscillations, due to the finite thickness of the film, indicate that these films are extremely flat with a thickness variation of only ∼ 20 Å over a length scale of several thousand angstroms. Using the constraint of epitaxy to grow metastable cuprates in the infinite layer structure, novel high-temperature superconducting structural families have been formed. In particular, epitaxially-stabilized (Ca,Sr)CuO2BaCuO2 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 superconductivity at Tc(onset) ∼ 70 K. These results show that pulsed-laser deposition and epitaxial stabilization have been used to effectively ‘engineer’ artificially-layered thin-film materials.