Electronic correlations and unconventional spectral weight transfer in BaFe$_{2-x}$Co$_{x}$As$_{2}$

TL;DR

This study uses infrared optics to analyze electronic correlations in BaFe$_{2-x}$Co$_{x}$As$_{2}$, revealing moderate correlations driven mainly by Hund's coupling, unaffected by phase transitions or doping.

Contribution

It demonstrates that Hund's coupling J is the main driver of electronic correlations in BaFe$_{2-x}$Co$_{x}$As$_{2}$, with correlations remaining stable across different phases.

Findings

Electronic correlations are moderately strong.

Spectral weight transfer is governed by Hund's coupling J.

Correlations do not significantly change across phase transitions.

Abstract

We report an infrared optical study of the pnictide high-temperature superconductor BaFe$_{1.84}$Co$_{0.16}$As$_{2}$ and its parent compound BaFe$_{2}$As$_{2}$. We demonstrate that electronic correlations are moderately strong and do not change across the spin-density wave transition or with doping. By examining the energy scale and direction of spectral weight transfer, we argue that Hund's coupling \emph{J} is the primary mechanism that gives rise to correlations.