The dual nature of As-vacancies in LaFeAsO-derived superconductors: magnetic moment formation while preserving superconductivity
Abstract
As-vacancies (VAs) in La-1111-systems, which are nominally non-magnetic defects, are shown to create in their vicinity by symmetry ferromagnetically oriented local magnetic moments due to the strong, covalent bonds with neighboring Fe atoms that they break. From microscopic theory in terms of an appropriately modified Anderson-Wolff model, we find that the moment formation results in a substantially enhanced paramagnetic susceptibility in both the normal and superconducting (SC) state. Despite the VAs act as magnetic scatterers, they do not deteriorate SC properties which can even be improved by VAs by suppressing a competing or coexisting commensurate spin density wave or its remnant fluctuations. Due to the induced local magnetic moments an s++-scenario in related systems is unlikely.
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