Importance of dxy orbital and electron correlation in iron-based superconductors revealed by phase diagram for 1111-system

TL;DR

This study explores how structural parameters, especially pnictogen height, influence superconductivity in LaFeAsO-based materials, highlighting the importance of the dxy orbital and electron correlations in the phase diagram of 1111-system superconductors.

Contribution

It reveals the critical role of pnictogen height and dxy orbital in determining superconducting pairing strength and phase behavior in iron-based superconductors.

Findings

Superconducting transition temperature is strongly affected by pnictogen height.

Transition from weak to strong coupling superconductivity correlates with increased pnictogen height.

The dxy hole Fermi surface is crucial in the strong coupling regime.

Abstract

The structural flexibility at three substitution sites in LaFeAsO enabled investigation of the relation between superconductivity and structural parameters over a wide range of crystal compositions. Substitutions of Nd for La, Sb or P for As, and F or H for O were performed. All these substitutions modify the local structural parameters, while the F/H-substitution also changes band filling. It was found that the superconducting transition temperature $T_{c}$ is strongly affected by the pnictogen height $h_{Pn}$ from the Fe-plane that controls the electron correlation strength and the size of the $d_{xy}$ hole Fermi surface (FS). With increasing $h_{Pn}$, weak coupling superconductivity switches to the strong coupling one where the $d_{xy}$ hole FS is crucially important.