Epitaxial growth and critical current density of thin films of YBa2Cu3O7−x on LaAlO3 substrates

Abstract
Thin films of the high‐temperature superconductor YBa2 Cu3 O7−x have been produced on (100) LaAlO3 substrates by coevaporation and furnace annealing. A 14‐μm‐wide and 400‐μm‐long constriction patterned on a 0.8‐μm‐thick film had a zero resistance transition temperature of 90 K, a transition width of 1.5 K, and a critical current density of 8×104 A cm2 at 77 K. Although x‐ray diffraction shows a definite c‐axis alignment normal to the substrate plane, further analysis reveals that c‐axis alignment in the substrate plane is also present. The detailed microstructural picture is revealed by transmission electron microscopy: a continuous layer, about 0.2 μm thick adjacent to the substrate, with c axis normal to the substrate plane, and the remaining top portion of the film, with the c axis in the film plane. In spite of the bilayer structure, the film remains epitaxial (the axes of the superconductor are parallel to the 〈100〉 directions of the substrate).