Orbital-spin ordering in the striped antiferromagnetic state of iron-based superconductors

TL;DR

This paper investigates the magnetic properties of iron-arsenides using LSDA+U, revealing multiple low moment states influenced by orbital hybridization and proposing that superconductivity involves an orbital-spin ordered state.

Contribution

It introduces a new understanding of low moment states in iron-based superconductors and links orbital hybridization and geometry to magnetic and superconducting properties.

Findings

Identification of multiple low moment states influenced by U

Orbital hybridization between Fe neighbors drives low moment states

Superconducting phase involves an orbital-spin ordered state with canceling moments

Abstract

The magnetic properties of iron-arsenides are investigated using the LSDA+U approach. In addition to one high moment state, we find that a positive U also produces two low moment states with m~0.4 $\mu_{B}$ and m~1.0 $\mu_{B}$. The electronic structures indicate that the low moment states originate in the strong orbital hybridization between antiferromagnetic Fe neighbors. Therefore, the geometry of the FeAs4 tetrahedron is crucial to the low moment states, which is the key to understand the negative pressure coefficient of Tc in LiFeAs. Finally, our theory suggests that the superconducting phase is an orbital-spin ordered state, where the orbital spin-moments cancel each other.