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

Abstract

We focus on the effect of ionic radius of lanthanides and the number of electrons in 4f orbitals on the superconducting temperature in 12442-type iron-based superconductors RbLn 2Fe4As4O2 (Ln = Sm and Ho). Electronic properties of RbSm2Fe4As4O2 and RbHo2Fe4As4O2 with the largest differences of ionic radii and numbers of electrons in 4f orbital, and the largest difference of superconducting temperatures by using first-principles calculations. We predict that the ground state of RbLn 2Fe4As4O2 is spin-density-wave-type in-plane striped antiferromagnet, and the magnetic moment around each Fe atom is about 2μ B. RbSm2Fe4As4O2 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 orbital of Fe, which proves that RbSm2Fe4As4O2 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 Fe2As2 bilayers. This is also confirmed by the charge density difference ρ(RbHo2Fe4As4O2) −ρ(RbSm2Fe4As4O2). It increases the internal coupling strength of the bilayer Fe2As2 layers, which in turn leads to a higher T c of RbSm2Fe4As4O2 than RbHo2Fe4As4O2. 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.