Role of Lanthanide in the Electronic Properties of RbLn 2Fe4As4O2 (Ln = Sm and Ho) Superconductors

We focus on the effect of ionic radius of lanthanides and the number of electrons in 4 f orbitals on the superconducting temperature in 12442-type iron-based superconductors Rb Ln 2 Fe 4 As 4 O 2 ( Ln = Sm and Ho). Electronic properties of RbSm 2 Fe 4 As 4 O 2 and RbHo 2 Fe 4 As 4 O 2 with the largest differences of ionic radii and numbers of electrons in 4 f orbital, and the largest difference of superconducting temperatures by using first-principles calculations. We predict that the ground state of Rb Ln 2 Fe 4 As 4 O 2 is spin-density-wave-type in-plane striped antiferromagnet, and the magnetic moment around each Fe atom is about 2 μ B . RbSm 2 Fe 4 As 4 O 2 has a great influence on the energy band near the Γ point, and a Dirac-like dispersion energy band appears. This band is mainly contributed by the d z 2 orbital of Fe, which proves that RbSm 2 Fe 4 As 4 O 2 has a stronger three-dimensionality. At the same time, this extra Fermi surface appears at the Γ point, which also shows that Sm can effectively enhance the coupling strength within Fe 2 As 2 bilayers. This is also confirmed by the charge density difference ρ (RbHo 2 Fe 4 As 4 O 2 ) − ρ (RbSm 2 Fe 4 As 4 O 2 ). It increases the internal coupling strength of the bilayer Fe 2 As 2 layers, which in turn leads to a higher T c of RbSm 2 Fe 4 As 4 O 2 than RbHo 2 Fe 4 As 4 O 2 . Determining the details of their electronic structure, which may be closely related to superconductivity, is crucial to understanding the underlying mechanism. Such microscopic studies provide useful clues for our further research of other high-temperature superconductors.