高压下122型铁基超导体的结构与物性研究

The 122 iron based superconductor is a kind of material that attract most attentions in the Iron based superconductor. In this project we will regulate the band gap with pressure, change the relative position of the Fermi level to control the carrier concentration. We will study the pressure induced superconductivity and explore the new quantum phenomenon induced by pressure. We will carry out synchrotron radiation research under high pressure to study the pressure effect on the crystalline lattice and the electronic structure. By the X-ray near edge absorption spectrum, we will determine the effective valence of the ion with pressure, which will help us to obtain useful information of electronic states of the 122 iron based superconductor. We will explore new iron based 122 system material by the high pressure synthesis method. We will make effort to improve the high temperature and high pressure synthesis process, to explore the high pressure synthesis regularities of 122 system.

“122”型是铁基超导体中最受关注的一类材料，在本项目中拟运用压力手段调节其带隙，通过改变费米面的相对位置来调控载流子浓度，研究压力对诱导超导电性的作用，探索压力诱导的量子序新现象。开展高压下同步辐射吸收谱的研究以及研究压力对结构的影响，研究材料中一部分离子在压力下的X射线吸收近边结构，通过确定其有效价态及其随着压力的变化，来获得122型铁基超导体电子态的重要信息。利用高压合成探索新的铁基122体系材料，改进高温高压合成工艺，探索122铁基体系的高压合成规律。

在对新型反铁磁材料Ca0.73La0.27FeAs2的研究中，通过一系列高压协同测量我们首次发现在反铁磁和超导相变临界压力和临界温度处存在双临界点，并观察到了压力诱导的反铁磁与超导之间的一级相变。实验结果表明，随着压力的增加，材料的反铁磁转变温度逐渐被抑制，在临界压力下，反铁磁转变温度突然消失，同时超导转变突然出现，并且超导转变起始温度与反铁磁转变消失的温度基本相同。这是首次在高温超导体中发现这种具有双临界点的反铁磁-超导转变相图， 为高温超导体机理的深入研究提供了新的实验结果。