液氮温区FeSe界面超导体的探索

In 2012, Chinese scientists first discovered that one unit cell FeSe film grown on oxide substrate by molecular beam epitaxy has a superconducting gap much larger than that of the bulk, and it persists to temperature above 65 K. These results were later confirmed by several other experimental groups, indicating that the interface between FeSe and oxides might be superconducting with Tc above the liquid nitrogen temperature (77 K). However, up to date there is no direct proof, such as zero resistance and Meissner effect, to show unambiguously that the FeSe/oxide interface enters the macroscopic superconducting state at liquid nitrogen temperature. In this project, we plan to explore the various factors that may affect the microscopic electronic structure and superconducting properties of the FeSe/oxides interface, aiming to find the optimal interface properties. Moreover, we will set up and optimize in situ four probe transport and mutual inductance magnetization measurements, which will give definitive evidence for the macroscopic superconducting transition temperature. We hope to provide unambiguous evidence that FeSe/oxides interface is indeed a high temperature superconductor with Tc above 77 K, which will represent a significant progress in the investigations of the superconducting mechanism and search for novel high Tc superconductors.

2012年，我国科学家率先发现在氧化物衬底上利用分子束外延技术生长的单层FeSe薄膜具有远大于体态的超导能隙，而且在65K的高温下其能隙依然存在。此后该结果被多个研究组所证实，意味着单层FeSe与氧化物界面超导体的转变温度可能超过液氮温度(77 K)。然而，至今还没有直接的实验证据，即零电阻和绝对抗磁性，确切证实FeSe/氧化物界面在液氮温区就进入宏观超导态。在本项目中，我们将从多方面探索各个自由度对FeSe/氧化物界面超导体系微观电子结构和超导性质的影响，进而寻找能够实现最高超导转变温度的最优界面。此外，我们将搭建并完善原位的四探针输运和交流互感抗磁性测量装置，从而可以直接标定该界面超导体的宏观超导转变温度。我们期望能够毫无异议地证实FeSe/氧化物界面存在液氮温区的高温超导电性，这将对研究高温超导机理和探索高温超导材料产生巨大推进作用。

非常好地完成了研究内容，实现了研究目标。我们从各个方面对FeSe/STO类界面超导进行了研究，基本确定其为s波超导体。此外，我们还成功搭建了超高真空原位交流互感抗磁性测量装置。发表了一系列高水平论文，达到了世界领先水平。共发表SCI论文30多篇，共发表SCI 论文30 多篇，包括2 篇Nature Materials，1 篇Nature Physics，3 篇PRL，2 篇PRX，1 篇Adv. Science。