Density functional study of orbital-selective magnetism in FeAs-based superconductors

TL;DR

This study uses density functional theory to analyze how different Fe d orbitals contribute to orbital-selective magnetism in LnFeAsO superconductors, revealing distinct mechanisms for antiferromagnetism and implications for superconductivity.

Contribution

It provides a detailed orbital-level understanding of magnetism in Fe-based superconductors, highlighting the different roles of dxy and dyz orbitals in magnetic behavior and their coupling to electronic structures.

Findings

dxy orbital-driven AFM is Fermi-surface nesting dependent

dyz orbital-driven AFM is superexchange mediated

d orbital characters influence superconductivity and magnetic coupling

Abstract

We performed spin-polarized density functional calculations of lanthanide-series (Ln) iron oxypnictides LnFeAsO (Ln=La, Ce, Pr, Nd, Sm, and Gd) with constrained Fe magnetic moments, finding that in-plane dxy and out-of-plane dyz orbital characters are preferred for small Fe magnetic moments. Comparison of LnFeAsO compounds shows that the antiferromagnetism (AFM) from the Fe dxy orbital is itinerantly driven by orbital-dependent Fermi-surface nesting while AFM from the Fe dyz orbital is driven by superexchange mechanism. The Fe magnetic moments of the two orbital characters show different coupling strengths to Fermi-surface electrons orbital-selectively, suggesting that they may play different roles in superconductivity and in AFM, and making d orbital characters of the magnetic moment resolvable by measuring the electronic structures.