Macroscopic persistent currents in laser ablated YBa2Cu3O7-x films

Abstract

Thin films of YBa2Cu3O7-x have been produced in situ by laser ablation. As the condensation of the superconducting film is done onto hot substrates (600-780°C) at high oxygen pressures (- 1 mbar), this techniques does not require any special postannealing step. Thus the total process time amounts to less than 10 min. Films were found to be polycrystalline with the c-axis preferentially oriented normal to the substrate plane on single crystalline (001) SrTiO3 and (random) Zr=2, as measured by ion channeling (Xmin = 5.5% on SrTiO3), x-ray scattering and TEM. Complete superconducting transitions above 90 K with transition widths of about 1 K have been observed even on YSZ substrates. Critical current densities, jc (77 K), of more than 2 x 10 6 A/cm2 could be obtained on SrTiO3-substrates. The high quality of the thin films over large areas was demonstrated by the measurement of persistent superconducting current densities at 77 K in the order of 10 5 A/cm2 in a 1.5 mm broad ring of 9 mm diameter. No dissipation of this persistent current could be observed during one hour. Measurement of the same film after 8 months in normal air showed a 40% decrease of jc and a stronger decrease of jc with an externed magnetic field, suggesting that in the meantime the macroscopic ring current density is dominated by intergranular weak links.