Dynamic correlation suppresses antiferromagnetism in heavily doped Fe-pnictide superconductor LaFeAsO1-xFx

Abstract

LaFeAsO is a prototypical iron pnictide that exhibits stripe antiferromagnetism in its parent form and evolves into an unconventional superconductor upon fluorine doping, with transition temperatures reaching ∽41 K. The microscopic origin of the suppression of antiferromagnetism with doping, however, remains under debate, with chemical pressure effects often invoked as the primary mechanism. Here, we revisit this problem using a combination of density functional theory (DFT), DFT+U, hybrid functional approaches, and ab initio dynamical mean-field theory (DFT+DMFT). Taking LaFeAsO_1-xF_x at x = 0.5 as a representative heavily doped case, we demonstrate that chemical pressure alone is insufficient to fully suppress the antiferromagnetic state within static mean-field descriptions. In contrast, DFT+DMFT calculations reveal a collapse of long-range antiferromagnetic order at ∽58 K, just above the superconducting transition temperature, while the undoped compound retains robust magnetic order. This suppression is accompanied by a pronounced sharpening of the quasiparticle peak and a reduction in incoherent scattering, indicative of enhanced electronic coherence upon doping. Our results highlight the essential role of dynamical correlation effects, beyond one-electron and static mean-field approximations, in driving the suppression of magnetism in fluorine-doped LaFeAsO.