Anisotropic nonmonotonic behavior of the superconducting critical current in thin YBa_2Cu_3O_(7-δ) films on vicinal SrTiO_3 surfaces

摘要

The critical current density of epitaxial YBa_2Cu_3O_(7-δ) (YBCO) films grown on vicinal SrTiO_3 substrates was investigated by electrical transport measurements along and across the steps of the SrTiO_3 surface for a range of temperatures of 10 to 85 K and in applied magnetic fields varying from 0 to 14 T. For vicinal angles of 4° and 8°, we found evidence of enhanced pinning in the longitudinal direction at low magnetic fields for a wide region of temperatures and attribute this phenomenon to antiphase boundaries in the YBCO film. The transverse J_c data showed a peak in the J_c (H) curve at low magnetic fields, which was explained on the basis of magnetic interaction between Abrikosov and Abrikosov-Josephson vortices. The in-plane J_c anisotropy observed for vicinal angles of 0.4° was reversed with respect to the 8° and 4° samples. This phenomenon was interpreted on the basis of strain induced in the YBCO film by the stepped substrate's surface.