AUTHOR=Yu Rong , Hu Haoyu , Nica Emilian M. , Zhu Jian-Xin , Si Qimiao 

TITLE=Orbital Selectivity in Electron Correlations and Superconducting Pairing of Iron-Based Superconductors

JOURNAL=Frontiers in Physics

VOLUME=Volume 9 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2021.578347

DOI=10.3389/fphy.2021.578347

ISSN=2296-424X

ABSTRACT=Electron correlations play a central role in iron-based superconductors. In these systems, multiple Fe $3d$-orbitals are active in the low-energy physics, and they are not all degenerate. For these reasons,  the role of orbital-selective correlations has been an active topic in the study of the iron-based systems. In this paper, we survey the recent developments on the subject. For the normal state, we emphasize the orbital-selective Mott physics that has been extensively studied, especially in the iron chalcogenides, in the case of  electron filling $n \sim 6$. In addition, the interplay between orbital selectivity and electronic nematicity is addressed. For the superconducting state, we summarize the initial ideas for orbital-selective pairing, and discuss the recent explosive activities along this direction. We close with some perspectives on several emerging topics. These include  the evolution of the orbital-selective correlations, magnetic and nematic orders and superconductivity as  the electron filling factor is reduced from $6$ to $5$, as well as the interplay between electron correlations and topological bandstructure in iron-based superconductors.