Multilayered structures of (RE = rare earth)Ba_2Cu_3O_x films: an approach for the growth of superior quality large-area superconducting films on sapphire substrates

摘要

Relatively thick REBa_2Cu_3O_(7-delta) (RE = rare earth) films (thickness approx 400-600 nm) with significantly improved surface morphology and critical current properties using a multilayered structure which alternates main layers of YBa_2Cu_3O_(7-delta) (YBCO) with intermediate DyBa_2Cu_3O_(7-delta) (DyBCO) layers on CeO_2-buffered sapphire substrates were investigated. The DyBCO layer, which has a close lattice matching with YBCO, functions as a good starting template for the growth of high-quality YBCO layers. Critical current density (J_c) drastically increased up to a factor of 2 for YBCO/DyBCO multilayer films, compared to YBCO monolayer films in both the self-field and applied magnetic field. The significant improvement in J_c is attributed to the improvement of surface smoothness and enhanced flux pinning properties as revealed by the magnetic-field angular dependence of J_c.