Structure and superconductivity in highly Cu-rich YBa₂Cu₃O_7-δ film

You-Sheng Chen^1*, Danru Qu^1,2, J. G. Lin^1,2

¹Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
²Center for Atomic Initiatives for New Materials, National Taiwan Universit, Taipei, Taiwan

* Presenter:You-Sheng Chen, email:youshengchen@ntu.edu.tw

In order to clarify the off-stoichiometry effect in high-T_C superconductor YBa₂Cu₃O_7-δ(YBCO) thin film, Cu-rich YBCO (Cu-YBCO) films were prepared with pulsed laser deposition by using a highly off-stoichiometric, Y: Ba: Cu = 1: 2: 4, target. X-ray diffraction showed an epitaxial growth of YBCO on each SrTiO₃, LaAlO₃ and LSAT substrates. High-resolution transmission electron microscope (HR-TEM) and electron dispersive spectroscopy (EDS) confirmed the epitaxial growth and the consistent off-stoichiometry through whole range of thickness. Interestingly, the large excess of Cu didn’t induce nanoparticle type of defects in the film. Instead, nano-size crystal domains with cubic symmetry were found epitaxially embed in the orthorhombic YBCO matrix. Comparing to the pure YBCO, the Cu-YBCO film exhibits considerably higher critical current and irreversibility field at liquid nitrogen temperature. The flux pining properties were revealed by power-law analysis which indicates a significant enhancement of thermal de-pining process. The improvement of superconducting properties together with the effective field tolerance promotes the potential applications of epitaxial type artificial pining center in YBCO thin film devices.

Keywords: High TC superconductor, Flux pinning, Thin-film, Pulse laser deposition