We analyze the electronic properties of the recently discovered stoichiometric superconductor ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ by combining an ab initio approach and a projection of the band structure to a low-energy tight-binding Hamiltonian, based on the maximally localized Wannier orbitals of the $3d$ Fe states. We identify the key symmetries as well as differences and similarities in the electronic structure between ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ and the parent systems ${\mathrm{CaFe}}_2{\mathrm{As}}_2$ and ${\mathrm{KFe}}_2{\mathrm{As}}_2$. In particular, we find ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ to have a significantly more quasi-two-dimensional electronic structure than the latter systems. Finally, we study the superconducting instabilities in ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ by employing the leading angular harmonics approximation and find two potential $A_{1g}$-symmetry representations of the superconducting gap to be the dominant instabilities in this system.

中文翻译：

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CaKFe4As4中的电子性质，低能哈密顿量和超导不稳定性

我们分析了最近发现的化学计量超导体的电子性质 ${\mathrm{磷酸铁钙}}_4{\mathrm{作为}}_4$通过从头算的方法和能带结构的投影到低能的紧束缚哈密顿量，这是基于最大定位的万尼尔轨道的$3d$铁的状态。我们确定了关键的对称性以及电子结构之间的区别和相似之处${\mathrm{磷酸铁钙}}_4{\mathrm{作为}}_4$ 和父系统 ${\mathrm{咖啡店}}_{\mathrm{2个}}{\mathrm{作为}}_{\mathrm{2个}}$ 和 ${\mathrm{钾铁}}_{\mathrm{2个}}{\mathrm{作为}}_{\mathrm{2个}}$。特别是，我们发现${\mathrm{磷酸铁钙}}_4{\mathrm{作为}}_4$具有比后者系统明显更多的准二维电子结构。最后，我们研究了超导不稳定性${\mathrm{磷酸铁钙}}_4{\mathrm{作为}}_4$ 通过采用超前角谐波近似并找到两个电势 ${\mathrm{一个}}_{\mathrm{1个}G}$超导间隙的对称表示是该系统中的主要不稳定性。