Superconducting Properties of Ultra-Thin Films of Y₁Ba₂Cu₃O_7-x

Abstract

We have grown ultra-thin films of Y₁Ba₂Cu₃O_7-x in situ on (001) SrTiO₃ by pulsed laser deposition. The zero resistance transition temperature (T_CO) is > 90 K for films > 300 Å thick. The critical current density (J_C at 77 K) is 0.8 × 10⁶ A/cm² for a 300 Å film and 4–5 × 10⁶ A/cm² for a 1000 Å film. The T_CO and J_C deteriorate rapidly below 300 Å, reaching values of 82 K and 300 A/cm² at 77 K, respectively, for a 100 Å film. Films only 50 Å thick exhibit metallic behavior and possible evidence of superconductivity without showing zero resistance to 10 K. These results are understood on the basis of the defects formed at the film-substrate interface, the density of which rapidly decreases over a thickness of 100 Å. We have studied these defects by ion channeling measurements and cross section transmission electron microscopy. Our results suggest that the superconducting transport in these films is likely to be two dimensional in nature, consistent with the short coherence length along the c-axis of the crystals.