Realization of epitaxial thin films of the superconductor K-doped BaFe2As2
Realization of epitaxial thin films of the superconductor K-doped BaFe2As2
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DOI：
10.1103/physrevmaterials.5.014801
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发表时间：
2021-01-05
影响因子：
3.4
通讯作者：
Yamamoto, Akiyasu
中科院分区：
文献类型：
--
作者：
Qin, Dongyi;Iida, Kazumasa;Yamamoto, Akiyasu
铁基超导体Ba₁₋ₓKₓFe₂As₂由于超导电线和块状永磁体方面的最新进展，正成为高磁场应用的关键材料。外延薄膜在研究和人工调控物理性质方面起着重要作用；然而，由于K的高挥发性，Ba₁₋ₓKₓFe₂As₂外延薄膜的合成仍然具有挑战性。在此，我们报道了通过分子束外延法，结合使用氟化物衬底（CaF₂、SrF₂和BaF₂）以及低温生长（350 - 420摄氏度）成功生长出外延Ba₁₋ₓKₓFe₂As₂薄膜。我们在CaF₂上生长的外延薄膜在起始临界温度为36 K时呈现出明显的超导转变，比块状晶体略低约2 K，这可能是由于晶格和热膨胀失配引起的应变效应。由磁化磁滞回线确定的临界电流密度（Jₑ）在自场下4 K时高达2.2 MA/cm²。薄膜的磁场下Jₑ特性优于块状晶体。外延薄膜的实现为通过外延应变调控超导性质以及揭示Ba₁₋ₓKₓFe₂As₂的本征晶界输运提供了机会。
The iron-based superconductor Ba1-xKxFe2As2 is emerging as a key material for high magnetic field applications owing to the recent developments in superconducting wires and bulk permanent magnets. Epitaxial thin films play important roles in investigating and artificially tuning physical properties; nevertheless, the synthesis of Ba1-xKxFe2As2 epitaxial thin films remained challenging because of the high volatility of K. Herein, we report the successful growth of epitaxial Ba1-xKxFe2As2 thin films by molecular-beam epitaxy with employing a combination of fluoride substrates (CaF2, SrF2, and BaF2) and a low growth temperature (350-420 degrees C). Our epitaxial thin film grown on CaF2 showed sharp superconducting transition at an onset critical temperature of 36 K, slightly lower than bulk crystals by similar to 2 K due presumably to the strain effect arising from the lattice and thermal expansion mismatch. Critical current density (J(c)) determined by the magnetization hysteresis loop is as high as 2.2 MA/cm(2) at 4 K under self-field. In-field J(c) characteristics of the film are superior to the bulk crystals. The realization of epitaxial thin films opens opportunities for tuning superconducting properties by epitaxial strain and revealing intrinsic grain boundary transport of Ba1-xKxFe2As2.Y