Epitaxial growth and critical current density of thin films of YBa2Cu3O7−<i>x</i> 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 cm−2 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).