新型低维强关联系统超导理论研究

High-temperature superconductivity (HTS) is of both scientific and practical importance, it has been a research focus in condensed matter physics for more than twenty years. However, due to the complexity and diversity of the high-temperature superconducting (SC) materials, the mechanism of HTS is still under debate. This program will study the theory of superconductivity in new types of low-dimensional and strongly correlated systems by focusing on the rececntly discovered iron-based superconductors and by conducting fundamental research on the symmetry of the SC order parameters (OPs), as well as on the interplay between magnetism and superconductivity, to reveal the mechanism of superconductivity in iron-based and even the whole family of high-temperature superconductors. Specifically, based on various symmetries of the SC OPs, we will investigate, both analytically and numerically, the effect of inhomogeneity induced by impurities and magnetic fields on the quasiparticle interference and spin dynamics; By comparing the theoretical results with the experimental data, we will be able to confirm the symmetry of the SC OPs, as well as the relations between magnetism and superdonductivity; By further improving the analytical and numerical methods, we may also propose some possible phenomena to be verified by future experiments. In this program we will use a unique numerical method to solve the BdG equations with large system size self-consistently, which will enable us to rigorously but not phenomenologically investigate the impurity effect and vortex states. This is a property that did not exist in previous works and will lay the groundwork both theoretically and numerically for studying the inhomogeneity in materials.

高温超导具有重要的科学意义和应用价值，二十多年以来一直是凝聚态领域的研究热点。然而，由于高温超导材料的复杂性和多样性，高温超导机理一直悬而未决。本项目以新型低维强关联系统的超导理论为研究对象，主要关注近期发现的铁基超导体，对其超导序参量对称性以及磁性与超导间的关联进行基础科学研究，以揭示铁基体系乃至整个高温超导家族的超导机理。具体内容包括：基于不同的超导序参量对称性，理论分析和数值模拟材料中由杂质和外加磁场所引起的不均匀性对准粒子相干和自旋动力学的影响；通过将计算结果与实验数据相比较，确定超导序参量对称性以及磁性与超导的联系；进一步完善理论和数值方法，预测可能出现的一些物理现象以待实验检验。本项目拟以独特的数值方法自洽地求解大尺寸条件下的BdG方程，从而严格地而非唯象地研究杂质效应和磁通涡旋态，这是之前的研究工作所不具备的特点，也为有效考察材料中的不均匀性奠定理论和数值基础。

对新型低维超导材料的研究，不论是对于高温超导物理本质的揭示，还是在实际应用方面，都是有重要的意义的。在本项目中，我们从理论上研究了这些新型低维超导材料中的杂质与磁场效应，并利用这些效应考察了这些材料中的超导配对对称性、超导机理及其它可能出现的一些物理现象。在此期间，我们不仅针对铁基超导体，还针对近期的热门材料Sr2RuO4、铋基超导体及Sr2IrO4等做了研究，取得了很好的研究成果，对新型低维材料的超导性质及拓扑性质的研究做出较大贡献，具有重要的理论意义。