铁硒基超导研究新进展:高质量(Li,Fe)OHFeSe单晶薄膜

单晶薄膜形态的高温超导材料对于相关基础科学研究和应用开发都极为重要.多带的铁基高温超导体往往呈现丰富的物理现象，并具有较高的超导临界参数.特别是近年发现的插层（Li，Fe）OHFeSe超导体，无论对高温超导机理还是应用研究而言，都日益受到重视，已成为铁基家族中重要的典型材料.但是，该化合物含有OH键，加热易分解.因此，现有的常规高温成膜技术均不适用于生长该薄膜材料.为解决这一生长难题，我们最近发明了基体辅助水热外延生长法，实现了超导薄膜制备技术上的突破.本文简要介绍用此软化学成膜技术首次成功制备出（Li，Fe）OHFeSe单晶薄膜.该薄膜材料具有优良的结晶质量和较高的超导临界参数，特别是其高的临界电流密度和上临界场对应用开发有实际价值.因此，（Li，Fe）OHFeSe超导单晶薄膜的成功合成，为机理研究和应用开发分别提供了重要的实验载体和备选材料.另外，该薄膜技术也有望应用于其他功能材料的探索与合成，尤其是对常规手段难以获取的材料更具重大价值.

New progress on FeSe-based superconductors: high-quality and high-critical-parameter (Li,Fe)OHFeSe thin film

High-quality superconducting thin films play an important role in the application and basic research of high-T_c superconductivity. In these aspects, iron-based superconductors feature the merits of rich physical phenomena and high superconducting critical parameters (including the transition temperature T_c, the upper critical field H_c2 and the critical current density J_c). The recently discovered high-T_c (Li,Fe)OHFeSe superconductor proves to be an important material for the studies of the mechanism and application of unconventional high-T_c superconductivity. However, due to the hydroxyl ion inherent in the compound, none of the conventional high-temperature synthesis methods is applicable for (Li,Fe)OHFeSe materials in bulk and thin film forms. Recently, by developing a hydrothermal ion-exchange technique, we have synthesized for the first time big and high-quality single crystals of (Li,Fe)OHFeSe (2015 Phys. Rev. B 92 064515). Here in this paper, we brief our most recent progress on growing a high-quality single-crystalline superconducting film of (Li,Fe)OHFeSe (2017 Chin. Phys. Lett. 34 077404). The film has been prepared on a LaAlO₃ substrate by a hydrothermal epitaxial method. The high crystalline quality of the film is verified by X-ray diffraction (XRD). The XRD measurements show a single (001) orientation with a small crystal mosaic of 0.22° in terms of the full width at half maximum of the rocking curve, as well as an excellent in-plane orientation revealed by the φ-scan of (101) plane. Its bulk superconducting transition temperature T_c of 42.4 K is determined by both zero electrical resistance and diamagnetism measurements. Based on systematic magnetoresistance measurements, the upper critical field H_c2 is estimated to be 79.5 T and 443 T for the magnetic field perpendicular and parallel to the ab plane, respectively. Moreover, a large critical current density J_c of a value over 0.5 MA/cm² is achieved at ~20 K. Such a (Li,Fe)OHFeSe film therefore is not only important for the fundamental research for understanding the high-T_c mechanism, but also promising for the applications in high-performance electronic devices and large scientific facilities such as superconducting accelerator.