Abstract
Using random-phase approximation spin-fluctuation theory, we study the influence of the hybridization between iron orbitals and pnictide orbitals on the superconducting pairing state in iron-based superconductors. The calculations are performed for a 16-orbital Hubbard-Hund tight-binding model of that includes the As- orbital degrees of freedom in addition to the Fe- orbitals and compared to calculations for a 10-orbital Fe- only model. In both models we find a leading pairing state and a subleading -wave state in the parent compound. Upon doping, we find that the state remains the leading state in the 16-orbital model up to a doping level of 0.475 electrons per unit cell, at which the hole Fermi-surface pockets at the zone center start to disappear. This is in contrast to the 10-orbital model, where the -wave state becomes the leading state at a doping of less than 0.2 electrons. This improved stability of pairing is found to arise from a decrease of orbital weight on the electron pockets due to hybridization with the As- orbitals and the resulting reduction of near spin-fluctuation scattering which favors the competing -wave state. These results show that the orbital dependent hybridization of Fermi-surface Bloch states with the usually neglected -orbital states is an important ingredient in an improved itinerant pairing theory.
- Received 11 May 2018
DOI:https://doi.org/10.1103/PhysRevB.98.024507
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