铁基超导体奇异轨道序、结构相变与超导电性的理论研究

项目名称： 铁基超导体奇异轨道序、结构相变与超导电性的理论研究

项目编号： No.11404163

项目类型： 青年科学基金项目

立项/批准年度： 2015

项目学科： 数理科学和化学

项目作者： 姚子健

作者单位： 南京师范大学

项目金额： 25万元

中文摘要： 作为最新发现的一类高温超导体，铁基超导体为人们理解高温超导现象提供了新的研究对象与视角。铁基超导体与铜氧化物高温超导体有很多相似之处：二维层状结构、磁性母体、对母体进行掺杂出现超导相。同时，由于铁基超导体的多轨道特性，轨道自由度与自旋自由度处于同等位置，在铁基超导体的超导电性中起重要作用。我们将在巡游电子模型的框架下，理解并阐述铁基超导体中由于轨道自由度与自旋自由度的耦合引致奇异密度波态的机制，以及相应的物理后果，讨论其与现有液晶相理论的异同。给出轨道涨落机制下超导电性的一系列物理性质，为实验上区分铁基超导体微观机制提供理论依据。通过多轨道模型解释一些体系中自旋密度波态与超导的共存现象。最后，我们将铁基超导体中发展的轨道序理论应用到其它与铜氧化物有相同结构的化合物中，解释相关物理现象。

中文关键词： 铁基超导体；自旋涨落；轨道有序；多轨道哈伯德模型

英文摘要： As the latest member of the family of high temperature superconductors, iron-based superconductors (FeSCs) provide us a new perspective to understand the mechanism of high temperature superconductivity. FeSCs share certain similarities with cuprates: two dimensional layered structure, antiferromagnetic parent compound, and the emergence of superconductivity with electron or hole doping. Meanwhile, due to the multi-orbital nature of FeSCs, the orbital degrees of freedom that are considered equally important as the spin degrees of freedom, play an essential role in the mechanism of superconductivity. In this project, starting with the scenario of itinerant electron picture, we will elaborate a novel density-wave state that is induced by the coupling between orbital and spin degrees of freedom, and its experimental consequences. Then we will discuss its relation to other theories that are based on nematic order. We will study the electronic properties of the orbital-fluctuation-induced superconductivity, which could be informative for determining the mechanism of superconductivity in FeSCs. We will study the coexistence of spin-density-wave state and superconductivity in certain systems. Furthermore, inspired by the studies of orbital physics in FeSCs, we will apply the multiorbital weak coupling theory to some compounds that are isostructural to cuprates, to explain the experimentally observed phenomena such as pseudogap and Fermi surface nesting induced orbital ordering.

英文关键词： iron-based superconductors;spin fluctuations;orbital ordering;multi-orbital Hubbard model