超导和铁磁是凝聚态物理中两种不同的、相互对立的宏观量子多体现象。两者在同一化合物中的竞争与共存可能产生许多新奇的物理性质，如自发磁通涡旋态、FFLO态等。我们最近发现的交互生长型铁基化合物AkEuFe4As4(Ak=Rb,Cs)同时具有超导和铁磁性质，为超导和铁磁的共存研究提供了更理想的研究平台。本项目主要以AkEuFe4As4为研究对象，一方面通过多元素位置的化学掺杂有效调节FeAs层“内禀”超导电性以及Eu层的“内磁场”，研究掺杂对超导和磁性的变化的影响以及超导和磁性的相互作用，重点研究可能存在的自发磁通涡旋、FFLO态等超导铁磁共存现象；另一方面，通过机械解离制备AkEuFe4As4 薄膜，探索其超导和磁性与薄膜厚度的关系，以及维度降低对其超导和磁性的影响。本项目的实施不但可以进一步理解超导与铁磁共存现象，同时也为铁磁超导体薄膜在器件方面的应用奠定一定的科学基础。

Superconductivity (SC) and ferromagnetism (FM) are two different and antagonistic macroscopic quantum many-body phenomena in condensed matter physics. The coexistence of the two phenomena in a single compound may produce various novel physical properties, such as FFLO state, spontaneous vortex state and SC enhancement. Recently, SC and FM are considered to coexist in the newly discovered inter-growth iron-based compound AkEuFe4As4(Ak=Rb,Cs), providing a more ideal platform to investigate the interplay of SC and FM. In the project, we will mainly study the AkEuFe4As4 (Ak = Rb, Cs) system. On the one hand, by the chemical doping at different sites to effectively tune the “intrinsic” superconducting parameters of the FeAs layers and the “internal field” of the Eu sublattice, we study the influence of doping on SC and magnetism, and the interplay of the two. We will focus on the possible FFLO state, spontaneous vortex state and SC enhancement in AkEuFe4As4 (Ak = Rb, Cs) system. On the other hand, exfoliated highly crystalline 2D AkEuFe4As4 (Ak = Rb, Cs) films with different thickness will be studied in terms of the relation of the film thickness and its SC and magnetism, mainly the influence of lowered dimension on the two. The project will contribute to further understanding the interplay of SC and magnetism in ferromagnetic superconductors and, moreover, lay a scientific foundation for the possible application of iron-based ferromagnetic superconducting films in devices.