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Nanostructured epitaxial thin films of Fe-based superconductors with enhanced superconducting properties P. Mele1, K. Matsumoto2,7, H. Nagayoshi2, K. Fujita2, Y. Yoshida3,7, Y. Ichino3,7, T. Kiss4,7, A. Ichinose5,7, M. Mukaida6,7, B. Maiorov8, F.F. Balakirev8, S.A. Baily8and L. Civale8 1

Institute for Sustainable Science and Development, Hiroshima University, Kagamiyama 1-3-1 Higashi-Hiroshima 739-8530, Japan 2 Department of Materials Science and Engineering, Kyushu Institute of Technology, 1-1 Sensuicho, Tobata-ku, Kitakyushu 804-8550, Japan 3 Department of Energy Engineering and Science, Nagoya University, Furo-cho, Chikikusa-ku, Nagoya 464-8603, Japan 4 Department of Electrical and Electronic Systems Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 812-8581, Japan 5 Electric Power Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanazawa 240-0196, Japan 6 Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 812-8581, Japan 7 JST-TRIP, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan 8 MPA-NHMFL and MPA-STC, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

ABSTRACT Epitaxial Fe-Te-Se thin films were deposited by pulsed laser deposition at 250 ~ 600 °C on SrTiO3 (100, STO), MgO (100), LaAlO3 (100, LAO) and CaF2 (100) single crystal substrates. Best superconducting film was grown on CaF2: Tconset = 20.0 K and Tc0 = 16.18 K with Tdep = 300 °C, 45000 pulses, 3 Hz. The critical current density Jc at 4.2 K was 0.41×106A/cm2 at 0 T and 0.23×106 A/cm2 at 9 T. Angular dependence of Jc showed broad c-axis correlated peak when B ≥ 3 T. INTRODUCTION The discovery of superconductivity in iron-pnictides materials [1] has generated a tremendous interest in the scientific community and a huge amount of papers on sintered samples was published (see [2] and references therein). The new superconductors were categorized in four main families: “1111” (such as the primarily discovered LaFeAsO0.89F0.11 [1] and derived compounds), “111” (like LiFe1-xAs [3]), “122” (like BaFe2As2 [4]) and the simplest “11” family (like FeSe1-x [5]). Development of research on highly crystalline samples (single crystals and especially thin films) is greatly desired to enlighten the fundamental physical properties of Febased superconductors and to disclose them to applications. Overcoming the initial difficulties related to tendency of As to volatilize during the pulsed laser ablation, several high-quality

epitaxial films belonging to 122 family were reported [6-9].Critical currents which values are quite larger than the values obtained in single crystals with the same composition were achieved [8, 9]. Even if their Tc is low compared with 1111 or 122 families, the compounds of 11 family appear attractive at least for two aspects: one is synthesis, because the poisonous and volatile As element is absent; the other one is the challenge of practical applications because upper critical field Bc2(0) is quite high approaching 50