Fabrication of Fe(Te,Se) films added with oxide or chalcogenide: Influence of added material on phase formation and superconducting properties

Incorporation of a dopant, an impurity, and a non-superconducting second phase in superconducting films is an important approach to control the superconducting property. In spite of extensive studies on the oxide superconducting nanocomposite films, the influence of additive materials on the phase formation and nanostructure is unclear in the iron based superconducting chalcogenide, Fe(Te,Se). Here, the incorporation of oxide or chalcogenide in Fe(Te,Se) films using pulsed laser deposition was investigated. When TiO2, Fe2O3, Yb2O3, CeO2, Nb2O5, SnSe, or SnTe was added, c axis oriented Fe(Te,Se) films were not formed. On the other hand, c axis oriented Fe(Te,Se) films were obtained when SrTiO3 was added at the content of 3–10 areal% and the deposition temperature of 400–550 °C. While a characteristic nanostructure originating from SrTiO3 was not observed for the small SrTiO3 content (3%), the nanocomposite structure comprising of nanocolumns was formed for the large SrTiO3 content (10%). The critical temperature was 8.2–8.6 K in the Fe(Te,Se) + SrTiO3(3%) thin films deposited at 500 °C, while the critical temperature was ∼10 K in the Fe(Te,Se) films. The irreversibility curve behavior was varied by the structural change in the natural pinning centers, which resulted from the SrTiO3 addition, while the pinning effect by the nanocomposite structure was concealed by the Tc degradation in the case of the large amount of SrTiO3 addition. Considering the dependence of the film structure on the additive material and the incorporation content, the superconducting properties of Fe(Te,Se) films should be designed.