Control of threading dislocation formation in epitaxially grown YBa2Cu3O7 thin films and their pinning properties

Abstract

To improve the critical current density of c-axis oriented YBa2Cu3O7 (YBCO) thin films, much effort has been devoted to the introduction of pinning centers that disrupt vortex migration under magnetic fields. Threading dislocations are anticipated to act as one-dimensional pinning centers without reducing the superconducting regions. In this study, YBCO thin films were prepared on a SrTiO3 (STO) + xCeO2 (x = 0%, 30%, and 50%) buffer layer by pulsed-laser deposition, and their nanostructures were analyzed by transmission electron microscopy. The interface between the buffer layer and the YBCO thin film was flat for the pure STO, while it was roughened by numerous nanoparticles for the CeO2-doped buffer layer. Due to these nanoparticles, threading dislocations were introduced more densely in the YBCO films on the STO + CeO2 buffer layer than in those on the pure STO buffer layer, depending on the volume percent of CeO2. Investigations of the critical current density as a function of the magnetic field revealed that the threading dislocations effectively act as pinning centers.