Anisotropic quasiparticle coherence in nematic BaFe$_2$As$_2$ studied with strain-dependent ARPES

TL;DR

This study investigates how strain affects quasiparticle coherence and spectral weight in nematic BaFe$_2$As$_2$, revealing orbital-dependent coherence differences that are relevant for understanding nematic order in iron-based superconductors.

Contribution

It combines in situ strain tuning with ARPES to analyze nematic response, highlighting orbital-dependent quasiparticle coherence changes in BaFe$_2$As$_2$.

Findings

The $d_{xz}$ band gains spectral weight under negative strain.

Quasiparticle coherence differs between $d_{xz}$ and $d_{yz}$ orbitals.

Results support a Hund's metal picture with orbital-dependent coherence.

Abstract

The hallmark of nematic order in iron-based superconductors is a resistivity anisotropy but it is unclear to which extent quasiparticle dispersions, lifetimes and coherence contribute. While the lifted degeneracy of the Fe $d_{xz}$ and $d_{yz}$ dispersions has been studied extensively, only little is known about the two other factors. Here, we combine in situ strain tuning with ARPES and study the nematic response of the spectral weight in BaFe$_2$As$_2$. The symmetry analysis of the ARPES spectra demonstrates that the $d_{xz}$ band gains quasiparticle spectral weight compared to the $d_{yz}$ band for negative antisymmetric strain $\Delta \epsilon_{yy}$ suggesting the same response inside the nematic phase. Our results are compatible with a different coherence of the $d_{xz}$ and $d_{yz}$ orbital within a Hund's metal picture. We also discuss the influence of orbital mixing.