新型有机超导体–金属掺杂稠环芳烃化合物的电子结构和磁性

The electronic structure and magnetic properties of superconductor in normal state are the basis to investigate the mechanism of superconductivity. For the metal-intercalated aromatic superconductor discovered recently, there are some controversies about the crystal structure of these materials between theoretical simulation and experiment measurement, as well as different theoretical results. No theoretical research is involved to study the distribution of local moments over the aromatic molecule, the formation of local moment and other magnetic properties. So, the crucial problem to be solved presently is to determine the reasonable crystal structure, electronic structure and magnetic properties in the ground state. We select the K or Ca intercalated phenanthrene and picene molecular crystals as the representative compounds and adopt the electronic structure simulation method based on the density function theory in this project, and the mainly researching contents are showed as below: to optimize the structure of K or Ca intercalated phenanthrene and picene molecular crystals, and check the structure through the simulation of X-ray diffraction pattern and Raman spectra; to clarify the distribution of local moments over the aromatic molecule and the formation mechanism of local moment; to explain the reason of anomaly change of crystal constants and local moment after doping metal atoms; to examine the effect of different doping concentrations of metal atom, doping different metal atoms, pressure, and substitution of CH group by N atom on the electronic structure, and search key features of the electronic and magnetic properties related to superconductivity. Through this research project, we can obtain the correct electronic structure and magnetic properties, then to provide an important scientific basis for the further study of the pairing mechanism in the metal-intercalated aromatic superconductor.

正常态的电子结构和磁性是研究超导配对机制的前提和基础。对于新发现的金属掺杂芳烃超导体，目前其晶体结构存在争议，基态磁性尚未明确，所以确定金属掺杂芳烃材料的晶体结构、基态磁性、电子结构已成为当前亟待解决的问题。本项目以钾、钙掺杂的苉和菲晶体为代表材料，借助电子结构模拟和理论分析等方法研究如下内容：采用不同的结构优化方案，并通过模拟其X射线衍射谱和Raman谱确定晶体结构；探明掺杂分子晶体的局域磁矩分布、局域磁矩形成机制和基态磁性；解释掺入钾后晶格常数和局域磁矩的反常变化；考察掺杂浓度、不同金属掺杂、外加压力、氮原子取代CH基团等因素对电子结构的影响，筛选出与超导电性有关的电子结构和磁性的关键特征。通过本项目的研究，可阐明该类超导材料正常态的电子结构和磁性，为进一步揭示其超导配对机理提供重要的科学依据。

芳烃有机超导体是近年刚发现的新型有机超导体，对丰富超导材料种类，扩展超导体的研究平台，扩充超导电性的物理内涵，揭示超导机制的起因都有着重大的科学意义。所以，其晶体结构、电子特性、磁性、超导机制等各种属性的研究成为当前凝聚态物理研究的重要课题。在本项目执行期内，依据项目任务书中的研究计划，完成了如下主要工作：1，用vdW-DFT方法研究了La掺杂phenanthrene， 确定了其晶体结构，强调了La的 d轨道电子对费米能级处态密度的贡献不可忽视。2，二价Ba掺杂的phenanthrene的计算中，从形成能，XRD谱等多角度表明Ba2phenanthrene是实验样品的主要成分，而不是实验中标明的Ba1.5phenanthrene，对实验有重要的指导意义，提出超导母体应是半导体的新观点。3，钾掺杂的picene晶体，表现出两个超导相Tc=7K和Tc=18K， 从掺杂浓度和晶体结构上揭示了两个超导相的产生原因，是进一步研究该材料的关键和基础。4，探索新的芳烃超导体方面，我们研究了二茂钴在压力下的电磁特性，没有发现超导现象，但发现是铁磁半金属。通过本项目的研究，基本从理论上确定了超导电性有关的晶体结构，阐明该类超导材料正常态的电子结构和磁性，找到了电子结构和磁性的关键信息，为进一步揭示其超导配对机理提供重要的科学依据和基础。