Coexistence of Itinerant Electrons and Local Moments in Iron-Based Superconductors

TL;DR

This paper proposes a model where itinerant electrons and local moments coexist in iron-based superconductors, explaining experimental observations such as magnetic susceptibility and superconductivity through their coupling.

Contribution

It introduces a minimal coupled model of itinerant electrons and local moments that accounts for key experimental features of iron-based superconductors.

Findings

The model explains the normal-state magnetic susceptibility behavior.

It accounts for the superconducting pairing mechanism.

The model aligns with experimental magnetic properties and isotope effects.

Abstract

In view of the recent experimental facts in the iron-pnictides, we make a proposal that the itinerant electrons and local moments are simultaneously present in such multiband materials. We study a minimal model composed of coupled itinerant electrons and local moments to illustrate how a consistent explanation of the experimental measurements can be obtained in the leading order approximation. In this mean-field approach, the spin-density-wave (SDW) order and superconducting pairing of the itinerant electrons are not directly driven by the Fermi surface nesting, but are mainly induced by their coupling to the local moments. The presence of the local moments as independent degrees of freedom naturally provides strong pairing strength for superconductivity and also explains the normal-state linear-temperature magnetic susceptibility above the SDW transition temperature. We show that this simple model is supported by various anomalous magnetic properties and isotope effect which are in quantitative agreement with experiments.