Substrate dependence of the superconducting properties of NdFeAs(O,F) thin films

• Published in: Solid state communications 2012-04, Vol.152 (8), p.735-739
• Main Authors: Uemura, Hiroki, Kawaguchi, Takahiko, Ohno, Toshiya, Tabuchi, Masao, Ujihara, Toru, Takeda, Yoshikazu, Ikuta, Hiroshi
• Format: Article
• Language: English
• Subjects: A. Fe-based superconductor; A. Thin film; B. Molecular beam epitaxy; Condensed matter: electronic structure, electrical, magnetic, and optical properties; D. Substrate dependence; Effects of material synthesis, crystal structure, and chemical composition; Exact sciences and technology; Low tc films; Physics; Superconducting films and low-dimensional structures; Superconductivity; Transition temperature variations
• ISSN: 0038-1098; 1879-2766
• DOI: 10.1016/j.ssc.2012.01.037

NdFeAs(O,F) superconducting thin films were grown on MgO, GaAs, CaF2, and LaAlO3 single crystal substrates by molecular beam epitaxy. All thin films exhibited a clear superconducting transition, while the critical temperature Tc showed a distinct substrate dependence, although the same growth condition was employed for all samples. The difference in Tc can be attributed to the lattice strain effect and how susceptible the substrate is to fluorine. The thin film grown on CaF2 substrate showed the highest Tc with an onset Tc of 56 K and zero resistance at 52 K. A correlation between Tc and the lattice constant ratio c/a was observed similar to what was reported for other iron-based superconductors, suggesting an intimate relation between the crystal structure and the superconducting properties. ► NdFeAs(O,F) superconducting thin films were grown on various substrates by MBE. ►Tc depended on the substrate, although the same growth condition was employed. ► The dependence cannot be understood in terms of a simple lattice strain effect. ► The thin film grown on CaF2 exhibited a high Tc of 56 K (onset). ► A correlation between Tc and the lattice constant ratio c/a was observed.