Orbital selective pairing and gap structures of iron-based superconductors

TL;DR

This paper explores how orbital selectivity influences spin-fluctuation pairing in iron-based superconductors, leading to better understanding of their anisotropic gap structures and the role of strong correlations.

Contribution

It introduces the concept of orbital selective Cooper pairing, incorporating reduced quasiparticle coherence to improve the itinerant pairing theory for Fe-based superconductors.

Findings

Orbital selectivity modifies spin-fluctuation pairing mechanisms.

The theory aligns well with experimental gap structures in FeSe and LiFeAs.

Orbital selective pairing is crucial in strongly correlated iron-based superconductors.

Abstract

We discuss the influence on spin-fluctuation pairing theory of orbital selective strong correlation effects in Fe-based superconductors, particularly Fe chalcogenide systems. We propose that a key ingredient for an improved itinerant pairing theory is orbital selectivity, i.e., incorporating the reduced coherence of quasiparticles occupying specific orbital states. This modifies the usual spin-fluctuation via suppression of pair scattering processes involving those less coherent states and results in orbital selective Cooper pairing of electrons in the remaining states. We show that this paradigm yields remarkably good agreement with the experimentally observed anisotropic gap structures in both bulk and monolayer FeSe, as well as LiFeAs, indicating that orbital selective Cooper pairing plays a key role in the more strongly correlated iron-based superconductors.