The orbital characters of bands in iron-based superconductor BaFe1.85Co0.15As2

TL;DR

This study maps the orbital characters of bands in BaFe1.85Co0.15As2, revealing discrepancies with theoretical predictions and highlighting the need for improved models of iron-based superconductors.

Contribution

It provides a comprehensive experimental analysis of orbital characters in BaFe1.85Co0.15As2, challenging existing theoretical band structure calculations.

Findings

Orbital distributions of $d_{xz}$, $d_{yz}$, and $d_{3z^2-r^2}$ agree with density functional theory.

Distributions of $d_{xy}$ and $d_{x^2-y^2}$ orbitals show significant disagreement with theory.

Results highlight the inadequacy of current band structure calculations for iron pnictides.

Abstract

The unconventional superconductivity in the newly discovered iron-based superconductors is intimately related to its multi-band/multi-orbital nature. Here we report the comprehensive orbital characters of the low-energy three-dimensional electronic structure in BaFe$_{1.85}$Co$_{0.15}$As$_2$ by studying the polarization and photon energy dependence of angle-resolved photoemission data. While the distributions of the $d_{xz}$, $d_{yz}$, and $d_{3z^2-r^2}$ orbitals agree with the prediction of density functional theory, those of the $d_{xy}$ and $d_{x^2-y^2}$ orbitals show remarkable disagreement with theory. Our results point out the inadequacy of the existing band structure calculations, and more importantly, provide a foundation for constructing the correct microscopic model of iron pnictides.