Role of Lanthanide in the Electronic Properties of RbLn_(2)Fe_(4)As_(4)O_(2)(Ln=Sm and Ho)Superconductors

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_(2)Fe_(4)As_(4)O_(2)(Ln=Sm and Ho).Electronic properties of RbSm_(2)Fe_(4)As_(4)O_(2) and RbHo2Fe4As4O2with the largest differences of ionic radii and numbers of electrons in 4f orbital,and the largest difference of superconducting temperatures by using firstprinciples calculations.We predict that the ground state of RbLn_(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 2μB.RbSm_(2)Fe_(4)As_(4)O_(2)has a great influence on the energy band near theΓpoint,and a Dirac-like dispersion energy band appears.This band is mainly contributed by the dz2orbital of Fe,which proves that RbSm_(2)Fe_(4)As_(4)O_(2)has a stronger threedimensionality.At the same time,this extra Fermi surface appears at theΓpoint,which also shows that Sm can effectively enhance the coupling strength within Fe2As2bilayers.This is also confirmed by the charge density differenceρ(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)As2layers,which in turn leads to a higher Tcof 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 hightemperature superconductors.