Self-doping effect and possible antiferromagnetism at titanium-layers in the iron-based superconductor Ba2Ti2Fe2As4O
Abstract
The electronic structure of Ba2Ti2Fe2As4O, a newly discovered superconductor, is investigated using first-principles calculations based on local density approximations. Multiple Fermi surface sheets originating from Ti-3d and Fe-3d states are present corresponding to the conducting Ti2As2O and Fe2As2 layers respectively. Compared with BaFe2As2, sizeable changes in the related Fermi surface sheets indicate significant electron transfer (about 0.12e) from Ti to Fe, which suppresses the stripe-like antiferromagnetism at the Fe sites and simultaneously induces superconductivity. Our calculations also suggest that an additional N\'eel-type antiferromagnetic instability at the Ti sites is relatively robust against the electron transfer, which accounts for the anomaly at 125 K in the superconducting Ba2Ti2Fe2As4O.
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