Anomalous Magnetic Susceptibility in Iron Pnictides: Paramagnetic Phase

TL;DR

This paper investigates the anomalous magnetic susceptibility in iron pnictides' paramagnetic phase, linking it to fluctuational spin correlations in a strongly correlated metallic state, explained via LDA+DMFT.

Contribution

It provides a quantitative understanding of anomalous susceptibility and spin gap features in doped Fe-pnictides using LDA+DMFT, supporting a Mottness-based scenario.

Findings

Anomalous temperature dependence of spin susceptibility observed.

Spin gap in NMR consistent with fluctuational spin correlations.

LDA+DMFT explains these features quantitatively.

Abstract

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.