Luca de' Medici, Gianluca Giovannetti, Massimo Capone
The discovery of high-Tc superconductivity in iron pnictides has opened a new path towards the understanding of this phenomenon. In the cuprates, the materials with the highest Tc, electron-electron interactions are the unifying element between the anomalies of the metallic state to the mechanism of superconductivity. In the iron family a likely electronic (magnetic) superconducting pairing is not accompanied by a distinctive evidence of strong correlations. Here we show that the experimental phase diagram of electron- and hole-doped BaFe2As2 can be unified - the stochiometric valence of 6 electrons per iron playing no special role for correlations - and that these materials are influenced by a Mott insulating state that would be realized at a doping of one hole/Fe (i.e. for half-filled conduction bands). The key factor is a strong Hund's coupling, which decouples the different orbitals. Each orbital behaves as a single band model, where the correlation degree only depends on how doped is each orbital from half-filling. As a result weakly and strongly correlated conduction electrons coexist in much of the phase diagram, an effect which increases with hole doping. This reconciles contrasting evidences on the electronic correlation strength and places the superconducting phase around 20% average doping per orbital from a half-filled Mott insulator, as in the cuprates.
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http://arxiv.org/abs/1212.3966
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