缺陷态及含铋层状超导体超导电性机制的理论与实验研究

The bismuth-containing layered superconductors are newly developed superconducting materials, which are obtained mainly through the chemical doping of the anti-ferromagnetic semiconductors or half-metals. Due to the strong spin-orbit coupling effect of the two dimensional bismuth network, these materials are considered to have novel topological superconductivity properties, which have attracted widespread attentions. However, because of their complex chemical compositions and diverse defect configurations, the understanding of the superconductivity mechanism and the search for new bismuth-containing layered superconductors with high Tc have become interesting, however difficult problems. By using the state-of-the-art first-principles calculations and experimental means, this project focuses on the study of the structural topology rules at the atomic length scale of the bismuth-containing layered superconductors, and aims to establish the fundamental structural constructing principles. This project also plans to study the detailed interactions between the defects and the matrix, and to explore the universal existence and the existing forms of the “superconducting functional motif”, in order to reveal the superconductivity mechanism induced by defects. On these basis, we use experimental means to search for new type of bismuth superconducting materials. The goal of this project is to understand the roles of defects in inducing the superconductivity, and to attempt to find some new structural rules for understanding and synthesizing new unconventional superconductors with high Tc.

含铋层状超导体是新近发展的超导体系，主要通过对反铁磁的半导体或半金属进行化学掺杂获得。由于二维层状铋网格有着强自旋轨道耦合效应，相关体系被认为可能具有拓扑超导属性，从而引起人们的广泛关注。但由于含铋层状超导体的化学组成复杂、缺陷构型多，如何设计新型层状超导体以及理解其相关超导电性机制是当前研究的重点问题。本项目拟联合第一原理计算模拟及相关实验手段，寻找含铋层状超导体原子尺度结构拓扑规律，提出该类材料基本构筑理论原则，实现其结构构筑从经验到理论的跨越。深入研究缺陷与基体间相互作用，探寻“超导功能基元”的普遍存在性及存在形式，揭示缺陷诱导超导电性的机制。在此基础上，设计并合成新型含铋超导材料，解决该类材料在结构设计中的关键问题，并为研究非常规超导体超导电性机制提供新的思路。

含铋层状超导体是新近发展的超导体系，主要通过对反铁磁的半导体或半金属进行化学掺杂获得。由于二维层状铋网格有着强自旋轨道耦合效应，相关体系被认为可能具有拓扑超导属性，从而引起人们的广泛关注。本项目采用第一原理计算系统地研究了一系列含铋正方格子的超导体以及含缺陷态的结构。完成了25种含铋正方格子层状超导体的拓扑学分类，对其结构特征做了归纳总结。基于平/陡带模型，对其中有代表性5种材料的Bi-6px，y轨道及其近邻原子轨道与材料超导性质之间的关系进行了分析总结。发展了一种新的用来快速筛选缺陷结构的高通量方法。通过构建大量的结构模型，确定了能量最优结构，首次发现并解释了缺陷体系的总能量与掺杂离子-空穴距离之间的对数关系，而非库仑关系，该关系可能适用于其他缺陷结构。在获得了Bi3O2SxCl、LaPb1-xBi2结构模型的基础上，计算了这些化合物的电子结构，从而确定了这些超导体中的超导功能基元。计算了一些材料的声子谱，研究了缺陷类型、浓度、位置等因素对电声耦合相互作用的影响。合成了新的名义组分为Y2O2.6Bi超导材料并进行了表征；建立并进一步优化了Nb3Al超导相的高效合成工艺。