Quantum dynamical screening of the local magnetic moment in Fe-based superconductors

TL;DR

This study uses advanced theoretical methods to analyze the dynamical screening of local magnetic moments in Fe-based superconductors, revealing the importance of vertex corrections for accurate susceptibility calculations.

Contribution

It introduces a detailed calculation of magnetic susceptibility incorporating vertex corrections, highlighting their role in capturing low-energy dynamical screening effects.

Findings

Vertex corrections are crucial for correct ω-dependence.

A low-energy peak at ~0.2 eV indicates dynamical screening.

Short-time magnetic moments are difficult to measure with typical neutron experiments.

Abstract

We have calculated the local magnetic susceptibility of one of the prototypical Fe-based superconductors (LaFeAsO) by means of the local density approximation + dynamical mean field theory as a function of both (imaginary) time and real frequencies with and without vertex corrections. Vertex corrections are essential for obtaining the correct $\omega$-dependence, in particular a pronounced low-energy peak at $\omega \sim 0.2 $eV, which constitutes the hallmark of the dynamical screening of a large instantaneous magnetic moment on the Fe atoms. In experiments, however, except for the case of x-ray absorption spectroscopy (XAS), the magnetic moment or the susceptibility represent typically the average over long time scales. In this respect, the frequency range of typical neutron experiments would be too limited to directly estimate the magnitude of the short-time moment.