Role of Lanthanides and Bilayer Fe(2)As(2) in the Electronic Properties of RbLn(2)Fe(4)As(4)O(2) (Ln = Gd, Tb, and Dy) Superconductors

The superconducting transition temperatures (T [Formula: see text]) of RbGd [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] , RbTb [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] , and RbDy [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] are 35 K, 34.7 K, and 34.3 K without doping, respectively. For the first time, we have studied the high-temperature nonmagnetic state and the low-temperature magnetic ground state of 12442 materials, RbTb [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] and RbDy [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] , using first principles calculations and comparing them with RbGd [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text]. We also performed a detailed study of the effects of lanthanides and bilayer Fe [Formula: see text] As [Formula: see text]. We predict that the ground state of RbLn [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] (Ln = Gd, Tb, and Dy) is spin-density-wave-type, in-plane, striped antiferromagnets, and the magnetic moment around each Fe atom is about 2 [Formula: see text]. We also found that the structural differences caused by the simple ionic radius have little effect on the properties of these three materials. Different lanthanide elements themselves play a major role in the electronic properties of the materials. It can be confirmed that the effect of Gd on RbLn [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] is indeed different from that of Tb and Dy, and the presence of Gd is more conducive to interlayer electron transfer. This means that Gd can transfer more electrons from the GdO layer to the FeAs layer compared to Tb and Dy. Therefore, RbGd [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] has a stronger internal coupling strength of the bilayer Fe [Formula: see text] As [Formula: see text] layer. This can explain why the T [Formula: see text] of RbGd [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] is slightly higher than that of RbTb [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text] and RbDy [Formula: see text] Fe [Formula: see text] As [Formula: see text] O [Formula: see text].