Li1-xFexOHFe1-ySe相关的新铁基超导体大尺寸单晶离子交换合成及物理机制研究

The fact that apparent physical properties of FeSe-based AyFe2-xSe2 superconductors differs from that of the iron arsenide ones has brought much controversy regarding whether a common underlying physics may govern both iron selenide and arsenide high-temperature superconductors. Recently, we have found that the hydrothermally synthesized (Li1-xFex)OHFe1-ySe (FeSe11111) superconductor exhibiting similar phase diagram to the iron arsenide superconductor. We therefore suggest that these two systems should be described by a common superconducting mechanism which closely relates to antiferromagnetic spin fluctuation. Therefore, FeSe11111 system, as a novel new superconducting member, will shed new light on unveiling the mechanism. However, its intrinsic electronic properties were lacking because only powder samples are obtainable via regular hydrothermal synthesis. Very recently, we have explored a novel hydrothermal ion-exchange technique and a high-quality (Li0.84Fe0.16)OHFe0.98Se big single crystal is successfully synthesized. In this project, we plan to, based on the results we achieved recently, systematically synthesize FeSe11111 big single crystals with various dopings and explore their intrinsic physical properties, and then complete the details of its phase diagram. On the other hand, we plan to explore new iron-based superconductors by varying intercalating blocks. By conducting this project, we will provide important experimental data and key information for exploring high quality iron-based new superconducting crystals as well as understanding its superconducting mechanism.

AxFe2-xSe2和FeAs基超导体表观物性差异很大，导致质疑其高温超导电性是否源于共同机制。最近我们发现水热合成的Li1-xFexOHFe1-ySe (FeSe11111) 超导体系呈现与FeAs基类似的物性相图，进而指出FeSe和FeAs基高温超导电性均源于相似的反铁磁涨落。因此，作为独特的新超导体系，FeSe11111为研究铁基高温超导机制提供了重要新契机。但通常的水热法只能制备粉末样品，其电子输运数据不能反映本征性质。目前我们又成功开发应用离子交换技术并首次制备了优质大尺寸最佳掺杂的FeSe11111高温超导单晶。本项目拟在此基础上，以新颖的水热离子交换技术合成系列掺杂的FeSe11111大尺寸单晶，并深入研究其本征物性包括反常的正常态性质及完善相图细节。同时选择不同插层团簇探索新铁基超导体。该项目将为探索合成新铁基超导体优质单晶和揭示铁基高温超导机制提供重要实验数据和关键信息。

FeSe 基超导体的超导临界温度可大范围调控, 物理现象丰富, 是非常规超导机理研究的热点。由于较高的超导临界参数及易于加工等特点, FeSe 基超导体在超导应用开发方面也日益受到重视。大尺寸高质量的单晶和薄膜形态的FeSe 基超导材料, 对于相关基础科学研究和应用开发都极为重要。在本项目的资助下，本研究围绕原计划的研究要点展开。首先，优化我们开发的水热离子交换和离子脱插技术，实现系列掺杂大尺寸(Li,Fe)OHFeSe和Tc可调的FeSe超导单晶的制备；接着，我们又发明了基体辅助水热外延生长方法, 成功解决了(Li,Fe)OHFeSe 超导体高质量薄膜的生长和物性调控难题。在此基础上，在相关物理问题的研究中取得新进展, 包括1）观测到(Li,Fe)OHFeSe 中的电子相分离现象，完善(Li,Fe)OHFeSe单晶的电子相图；2）在(Li,Fe)OHFeSe 单晶中实现Mn掺杂；3）发现(Li,Fe)OHFeSe 超导薄膜呈现很高的超导临界电流密度和上临界磁场, 其应用前景值得关注。此外，与国内外合作研究也取得一些重要进展。总之，通过本项目实施，取得了一些重要进展，为探索合成新铁基超导体优质单晶和揭示铁基高温超导机制提供了重要实验数据和关键信息。本项目实现了既定研究目标，并有所拓展。在SCI收录的科学期刊上发表和合作发表论文14篇，其中Nature Communications 1篇，PRB 5篇。