Orbital Selectivity in Hund's metals: The Iron Chalcogenides

TL;DR

This paper demonstrates that electron correlations induce a bad metallic state in FeSe and FeTe chalcogenides, with a crossover at U ≈ 2.5 eV, highlighting the role of Hund's coupling in orbital selectivity and coherence loss.

Contribution

It reveals a two-stage reduction of quasiparticle coherence driven by Hubbard U and Hund's J, establishing iron chalcogenides as Hund's correlated metals.

Findings

Crossover at U ≈ 2.5 eV in quasiparticle weight

Orbital dependence of quasiparticle weights emerges

Bad metallic state driven by Hund's coupling

Abstract

We show that electron correlations lead to a bad metallic state in chalcogenides FeSe and FeTe despite the intermediate value of the Hubbard repulsion $U$ and Hund's rule coupling $J$. The evolution of the quasi particle weight $Z$ as a function of the interaction terms reveals a clear crossover at $U \simeq$ 2.5 eV. In the weak coupling limit $Z$ decreases for all correlated $d$ orbitals as a function of $U$ and beyond the crossover coupling they become weakly dependent on $U$ while strongly depend on $J$. A marked orbital dependence of the $Z$'s emerges even if in general the orbital-selective Mott transition only occurs for relatively large values of $U$. This two-stage reduction of the quasi particle coherence due to the combined effect of Hubbard $U$ and the Hund's $J$, suggests that the iron-based superconductors can be referred to as Hund's correlated metals.