Thin and ultra-thin epitaxial films of YBa₂Cu₃O_7−δ deposited on LiNbO₃ substrates by pulsed excimer laser ablation

Abstract

We present here detailed transport, magnetic, structural and morphological studies on thin and ultra-thin films of superconducting YBa₂Cu₃O_7−δ (1-2-3) deposited on single crystalline substrates of LiNbO₃. The films were deposited using the technique of excimer laser ablation and have been found to have their c-axis oriented perpendicular to the plane of the film. We report results for films of thickness 500 Å, 1000 Å, 1600 Å and 6000 Å. Superconducting transition temperatures (T_c) have been studied by DC-resistivity, AC- and DC-magnetization. Critical current densities (J_c) from transport measurements are found to be in excess of 10⁵ A/cm² at 77 K. The temperature dependence of J_c is also examined and the flux pinning energy is estimated within the flux creep picture. High field hysteresis loop studies are in agreement with the above results and yield meaningful indications of critical fields H_c and irreversibility fields H_r. A study of the evolution of film morphology with increase of film thickness is also reported and it reflects on the growth mechanism of 1-2-3 on LiNbO₃.