Density Functional Study of ACa2Fe4As4F2 (A = K, Rb): Electronic Structure, Unconventional Superconductors

In this work, we have studied the structural and electronic properties of new-type of iron based superconductors ACa(2)Fe(4)As(4)F(2) (A = K, Rb) with first principles density functional theory based calculations. The density of states clearly shows that at Fermi level major contribution comes from iron 3d-orbitals and the contribution from other elements is very small. The electron-phonon coupling constant is found to be similar to 0.33 and similar to 0.4 for KCa2Fe4As4F2 and RbCa2Fe4As4F2, respectively. The estimated values of the upper bound of superconducting transition temperature is found to be similar to 2.4 K and similar to 4.2 K for KCa2Fe4As4F2 and RbCa2Fe4As4F2, respectively, suggesting that superconductingpairing mechanism in these systems have unconventional origin. Band structure calculations shows that ten bands crossesthe Fermi level and the corresponding Fermi surfaces show significant nesting with both hole-like and electron-like pockets.