Impact of Hund's rule on the physics of the Fe-based superconductors

The Hund's rule coupling J$_H$, as opposed to the Coulomb interaction (Hubbard) U, plays a dominating role in the Fe-based superconductors. The strong Hund's rule coupling combined with the multi-orbital nature and special valence of the Fe $3d$ shell, as well as the small crystal fields from the surroundings of an Fe atom, lead to many experimental consequences. In this talk, I will discuss the insights from first-principles calculations based on a combination of density functional theory and dynamical mean field theory. I will demonstrate the observable effects of \textit{Hundsness} on transport, optical conductivity, X-ray spectroscopy, angle-resolved photoemission spectroscopy, spin/magnetic excitations, and so on.\\[4pt] References:\\[0pt] [1] Z. P. Yin, K. Haule, and G. Kotliar,\textit{Nat. Mater.} {\bf 10}, 932-935 (2011).\\[0pt] [2] Z.P. Yin, K. Haule, and G. Kotliar,\textit{Nat. Phys.} {\bf 7}, 294-297 (2011).\\[0pt] [3] Z.P. Yin, K. Haule, and G. Kotliar, arXiv:1206.0801.\\[0pt] [4] Z.P. Yin, K. Haule, and G. Kotliar, unpublished.\\[0pt] [5] K. Haule and G. Kotliar,\textit{New J. Phys.} {\bf 11}, 025021 (2009).\\[0pt] [6] A. Kutepov, K. Haule, S. Y. Savrasov, and G. Kotliar, \textit{Phys. Rev. B} {\bf 82}, 045105 (2010).\\[0pt] [7] H. Park, K. Haule, and G. Kotliar, \textit{Phys. Rev. Lett.} {\bf107}, 137007 (2011).