Spin-charge-lattice couplings and Co doping effect in Ba(Fe 1−x Co x )2As2: an ab initio molecular dynamics study

Abstract

As one of the typical iron-based superconductors, Ba(Fe 1−x Co x )2As2 exhibits a dome-like evolution of superconducting transition temperature T c with the Co doping (x), which provides an ideal platform to explore the mechanism of unconventional superconductivity. Through ab initio molecular dynamics (AIMD) studies, we find that the spin, charge, and lattice degrees of freedom in Ba(Fe 1−x Co x )2As2 are intimately coupled with a characteristic frequency around 5.5 THz, which originates from the A1g phonon mode of the As atoms. Compared with the undoped BaFe2As2, the spin dynamics in Ba(Fe 1−x Co x )2As2 (x = 0.0625, 0.1250, 0.1875) shows enhanced spatial inhomogeneities, though the features of the charge dynamics are rarely modified. Along with the increasing Co doping, the spatial inhomogeneities of Fe spin dynamics display nonmonotonic changes, meanwhile the lattice vibrational spectra first show peak broadening and then restore the main peak around 5.5 THz, being both consistent with the nonmonotonic behavior of superconducting T c. Our study provides a molecular dynamics approach to investigate the couplings of spin, charge, and lattice in doped BaFe2As2, which could also be applied to explore the dome-like evolution of superconductivity in other Fe-based superconductors.