Orbital Selectivity in Hund's metals: The Iron Chalcogenides

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.