Observation of an anomalous temperature dependence of the spin susceptibility, along with a spin gap in NMR, in the quantum paramagnetic normal state of Iron Pnictides is a signature of an unusual metallic state. We argue that both these anomalous features are associated with a wide fluctuational regime dominated by dynamical, short-ranged and frustrated spin correlations in a strongly correlated metal. Using LDA+DMFT, we show that both these features can be quantitatively undertstood in the doped Fe-pnictides. We argue that such spin correlations naturally arise in a Mottness scenario, where an effective, dualistic description involves coexisting renormalized quasiparticles and effectively localized moments, arising from the same set of d bands.
@article{arxiv.0903.3732,
title = {Anomalous Magnetic Susceptibility in Iron Pnictides: Paramagnetic Phase},
author = {M. S. Laad and L. Craco},
journal= {arXiv preprint arXiv:0903.3732},
year = {2009}
}